plot¶

Plot lines, polygons, and symbols in 2-D

Synopsis¶

gmt plot [ table ] -Jparameters -Rwest/east/south/north[/zmin/zmax][+r][+uunit] [ -A[m|p|x|y] ] [ -B[p|s]parameters ] [ -Ccpt ] [ -Ddx/dy ] [ -E[x|y|X|Y][+a][+cl|f][+n][+wcap][+ppen] ] [ -F[c|n|r][a|f|s|r|refpoint] ] [ -Gfill ] [ -I[intens] ] [ -L[+b|d|D][+xl|r|x0][+yl|r|y0][+ppen] ] [ -N[c|r] ] [ -S[symbol][size[u] ] [ -U[stamp] ] [ -V[level] ] [ -W[pen][attr] ] [ -X[a|c|f|r][xshift[u]] ] [ -Y[a|c|f|r][yshift[u]] ] [ -Z[l|f]value ] [ -aflags ] [ -bibinary ] [ -dinodata ] [ -eregexp ] [ -fflags ] [ -ggaps ] [ -hheaders ] [ -iflags ] [ -lflags ] [ -pflags ] [ -ttransp ] [ -:[i|o] ] [ --PAR=value ]

Note: No space is allowed between the option flag and the associated arguments.

Description¶

Reads (x,y) pairs from files [or standard input] and will plot lines, polygons, or symbols at those locations on a map. If a symbol is selected and no symbol size given, then it will interpret the third column of the input data as symbol size. Symbols whose size is <= 0 are skipped. If no symbolsare specified then the symbol code (see -S below) must be present as last column in the input. If -S is not used, a line connecting the data points will be drawn instead. To explicitly close polygons, use -L. Select a fill with -G. If -G is set, -W will control whether the polygon outline is drawn or not. If a symbol is selected, -G and -W determines the fill and outline/no outline, respectively.

Required Arguments¶

-Jparameters (more …): Select map projection.

-Rxmin/xmax/ymin/ymax[+r][+uunit] (more …): Specify the region of interest.

For perspective view -p, optionally append /zmin/zmax. (more …)

Optional Arguments¶

table: One or more ASCII (or binary, see -bi[ncols][type]) data table file(s) holding a number of data columns. If no tables are given then we read from standard input.

-A[m|p|x|y]: By default, geographic line segments are drawn as great circle arcs. To draw them as straight lines, use the -A flag. Alternatively, add m to draw the line by first following a meridian, then a parallel. Or append p to start following a parallel, then a meridian. (This can be practical to draw a line along parallels, for example). For Cartesian data, points are simply connected, unless you append x or y to draw stair-case curves that whose first move is along x or y, respectively.

-B[p|s]parameters (more …): Set map boundary frame and axes attributes.

-Ccpt: Give a CPT or specify -Ccolor1,color2[,color3,…] to build a linear continuous CPT from those colors automatically, where z starts at 0 and is incremented by one for each color. In this case colorn can be a r/g/b triplet, a color name, or an HTML hexadecimal color (e.g. #aabbcc ). If -S is set, let symbol fill color be determined by the z-value in the third column. Additional fields are shifted over by one column (optional size would be 4th rather than 3rd field, etc.). If -S is not set, then it expects the user to supply a multisegment file where each segment header contains a -Zval string. The val will control the color of the line or polygon (if -L is set) via the CPT. If modern mode and no argument is given then we select the current CPT.

-Ddx/dy: Offset the plot symbol or line locations by the given amounts dx/dy [Default is no offset]. If dy is not given it is set equal to dx.

-E[x|y|X|Y][+a][+cl|f][+n][+wcap][+ppen]: Draw symmetrical error bars. Append x and/or y to indicate which bars you want to draw (Default is both x and y). The x and/or y errors must be stored in the columns after the (x,y) pair [or (x,y,z) triplet]. If +a is appended then we will draw asymmetrical error bars; these requires two rather than one extra data column, with the low and high value. If upper case X and/or Y are used we will instead draw “box-and-whisker” (or “stem-and-leaf”) symbols. The x (or y) coordinate is then taken as the median value, and four more columns are expected to contain the minimum (0% quantile), the 25% quantile, the 75% quantile, and the maximum (100% quantile) values. The 25-75% box may be filled by using -G. If +n is appended the we draw a notched “box-and-whisker” symbol where the notch width reflects the uncertainty in the median. This symbol requires a 5th extra data column to contain the number of points in the distribution. The +w modifier sets the cap width that indicates the length of the end-cap on the error bars [7p]. Pen attributes for error bars may also be set via +ppen. [Defaults: width = default, color = black, style = solid]. When -C is used we can control how the look-up color is applied to our symbol. Append +cf to use it to fill the symbol, while +cl will just set the error pen color and turn off symbol fill. Giving +c will set both color items.

-F[c|n|r][a|f|s|r|refpoint]: Alter the way points are connected (by specifying a scheme) and data are grouped (by specifying a method). Append one of three line connection schemes: c: Draw continuous line segments for each group [Default]. r: Draw line segments from a reference point reset for each group. n: Draw networks of line segments between all points in each group. Optionally, append the one of four segmentation methods to define the group: a: Ignore all segment headers, i.e., let all points belong to a single group, and set group reference point to the very first point of the first file. f: Consider all data in each file to be a single separate group and reset the group reference point to the first point of each group. s: Segment headers are honored so each segment is a group; the group reference point is reset to the first point of each incoming segment [Default]. r: Same as s, but the group reference point is reset after each record to the previous point (this method is only available with the -Fr scheme). Instead of the codes a|f|s|r you may append the coordinates of a refpoint which will serve as a fixed external reference point for all groups.

-Gfill (more …): Select color or pattern for filling of symbols or polygons [Default is no fill]. Note that this module will search for -G and -W strings in all the segment headers and let any values thus found over-ride the command line settings.

-Iintens: Use the supplied intens value (nominally in the -1 to +1 range) to modulate the fill color by simulating illumination [none]. If no intensity is provided we will instead read intens from the first data column after the symbol parameters (if given).

-L[+b|d|D][+xl|r|x0][+yl|r|y0][+ppen] Example

X
-L example

cat << EOF > t.txt
1 1
2 3
3 2
4 4
EOF
gmt begin filler pdf
gmt plot -R0/5/0/5 -JX3i -B t.txt -Gred -W2p -L+yb
gmt plot -B t.txt -Gred -W2p -L+yt -X3.25i
gmt plot -B t.txt -Gred -W2p -L+xl -X-3.25i -Y3.25i
gmt plot -B t.txt -Gred -W2p -L+xr -X3.25i
gmt plot -B t.txt -Gred -W2p -L+y4 -X-3.25i -Y3.25i
gmt plot -B t.txt -Gred -W2p -L+x4.5 -X3.25i
gmt end show: Force closed polygons. Alternatively, append modifiers to build a polygon from a line segment. Append +d to build symmetrical envelope around y(x) using deviations dy(x) given in extra column 3. Append +D to build asymmetrical envelope around y(x) using deviations dy1(x) and dy2(x) from extra columns 3-4. Append +b to build asymmetrical envelope around y(x) using bounds yl(x) and yh(x) from extra columns 3-4. Append +xl|r|x0 to connect first and last point to anchor points at either xmin, xmax, or x0, or append +yb|t|y0 to connect first and last point to anchor points at either ymin, ymax, or y0. Polygon may be painted (-G) and optionally outlined by adding +ppen [no outline].

-N[c|r]: Do NOT clip symbols that fall outside map border [Default plots points whose coordinates are strictly inside the map border only]. The option does not apply to lines and polygons which are always clipped to the map region. For periodic (360-longitude) maps we must plot all symbols twice in case they are clipped by the repeating boundary. The -N will turn off clipping and not plot repeating symbols. Use -Nr to turn off clipping but retain the plotting of such repeating symbols, or use -Nc to retain clipping but turn off plotting of repeating symbols.

-S[symbol][size[u]]

Plot symbols (including vectors, pie slices, fronts, decorated or quoted lines). If present, size is symbol size in the unit set in gmt.conf (unless c, i, or p is appended). If the symbol code (see below) is not given it will be read from the last column in the input data; this cannot be used in conjunction with binary input. Optionally, append c, i, or p to indicate that the size information in the input data is in units of cm, inch, or point, respectively [Default is PROJ_LENGTH_UNIT]. Note: if you provide both size and symbol via the input file you must use PROJ_LENGTH_UNIT to indicate the unit used for the symbol size or append the units to the sizes in the file. If symbol sizes are expected via the third data column then you may convert those values to suitable symbol sizes via the -i mechanism.

The uppercase symbols A, C, D, G, H, I, N, S, T are normalized to have the same area as a circle with diameter size, while the size of the corresponding lowercase symbols refers to the diameter of a circumscribed circle.

You can change symbols by adding the required -S option to any of your multisegment headers.

Choose between these symbol codes:

-S-

x-dash (-). size is the length of a short horizontal (x-dir) line segment.

-S+

plus (+). size is diameter of circumscribing circle.

-Sa

star. size is diameter of circumscribing circle.

-Sb[size[c|i|p|u]][+b[base]]

Vertical bar extending from base to y. The size is bar width. Append u if size is in x-units [Default is plot-distance units]. By default, base = 0. Append +b[base] to change this value. If base is not appended then we read it from the last input data column. Use +B[base] if the bar height is measured relative to base [Relative to origin].

-SB[size[c|i|p|u]][+b[base]]

Horizontal bar extending from base to x. The size is bar width. Append u if size is in y-units [Default is plot-distance units]. By default, base = 0. Append +b[base] to change this value. If base is not appended then we read it from the last input data column. Use +B[base] if the bar length is measured relative to base [Relative to origin].

-Sc

circle. size is diameter of circle.

-Sd

diamond. size is diameter of circumscribing circle.

-Se

ellipse. Direction (in degrees counter-clockwise from horizontal), major_axis, and minor_axis must be found in columns 3, 4, and 5.

-SE

Same as -Se, except azimuth (in degrees east of north) should be given instead of direction. The azimuth will be mapped into an angle based on the chosen map projection (-Se leaves the directions unchanged.) Furthermore, the axes lengths must be given in geographical instead of plot-distance units. An exception occurs for a linear projection in which we assume the ellipse axes are given in the same units as -R. For degenerate ellipses (circles) with just the diameter given, use -SE-. The diameter is excepted to be given in column 3. Alternatively, append the desired diameter to -SE- and this fixed diameter is used instead. For allowable geographical units, see Units [Default is k for km].

-Sfgap[/size][+l|+r][+b+c+f+s+t][+ooffset][+p[pen]].

Draw a front. Supply distance gap between symbols and symbol size. If gap is negative, it is interpreted to mean the number of symbols along the front instead. If size is missing it is set to 30% of the gap, except when gap is negative and size is thus required. Append +l or +r to plot symbols on the left or right side of the front [Default is centered]. Append +type to specify which symbol to plot: box, circle, fault, slip, or triangle. [Default is fault]. Slip means left-lateral or right-lateral strike-slip arrows (centered is not an option). The +s modifier optionally accepts the angle used to draw the vector [20]. Alternatively, use +S which draws arcuate arrow heads. Append +ooffset to offset the first symbol from the beginning of the front by that amount [0]. The chosen symbol is drawn with the same pen as set for the line (i.e., via -W). To use an alternate pen, append +ppen. To skip the outline, just use +p. Note: By placing -Sf options in the segment header you can change the front types on a segment-by-segment basis.

-Sg

octagon. size is diameter of circumscribing circle.

-Sh

hexagon. size is diameter of circumscribing circle.

-Si

inverted triangle. size is diameter of circumscribing circle.

-Sj

Rotated rectangle. Direction (in degrees counter-clockwise from horizontal), x-dimension, and y-dimension must be found in columns 3, 4, and 5.

-SJ

Same as -Sj, except azimuth (in degrees east of north) should be given instead of direction. The azimuth will be mapped into an angle based on the chosen map projection (-Sj leaves the directions unchanged.) Furthermore, the dimensions must be given in geographical instead of plot-distance units. For a degenerate rectangle (square) with one dimension given, use -SJ-. The dimension is excepted to be given in column 3. Alternatively, append the dimension diameter to -SJ- and this fixed dimension is used instead. An exception occurs for a linear projection in which we assume the dimensions are given in the same units as -R. For allowable geographical units, see Units [Default is k for km].

-Sk

kustom symbol. Append name/size, and we will look for a definition file called name.def in (1) the current directory or (2) in ~/.gmt or (3) in $GMT_SHAREDIR/custom. The symbol as defined in that file is of size 1.0 by default; the appended size will scale symbol accordingly. Users may add their own custom *.def files; see CUSTOM SYMBOLS below.

-Sl

letter or text string (less than 256 characters). Give size, and append +tstring after the size. Note that the size is only approximate; no individual scaling is done for different characters. Remember to escape special characters like *. Optionally, you may append +ffont to select a particular font [Default is FONT_ANNOT_PRIMARY] and +jjustify to change justification [CM].

-Sm

math angle arc, optionally with one or two arrow heads [Default is no arrow heads]. The size is the length of the vector head. Arc width is set by -W, with vector head outlines defaulting to half of arc width. The radius of the arc and its start and stop directions (in degrees counter-clockwise from horizontal) must be given in columns 3-5. See Vector Attributes for specifying other attributes.

-SM

Same as -Sm but switches to straight angle symbol if angles subtend 90 degrees exactly.

-Sn

pentagon. size is diameter of circumscribing circle.

-Sp

point. No size needs to be specified (1 pixel is used).

-Sq

quoted line, i.e., lines with annotations such as contours. Append [d|D|f|l|L|n|N|s|S|x|X]info[:labelinfo]. The required argument controls the placement of labels along the quoted lines. Choose among six controlling algorithms:

ddist[c|i|p] or Ddist[d|e|f|k|m|M|n|s]

For lower case d, give distances between labels on the plot in your preferred measurement unit c (cm), i (inch), or p (points), while for upper case D, specify distances in map units and append the unit; choose among e (m), f (foot), k (km), M (mile), n (nautical mile) or u (US survey foot), and d (arc degree), m (arc minute), or s (arc second). [Default is 10c or 4i]. As an option, you can append /fraction which is used to place the very first label for each contour when the cumulative along-contour distance equals fraction * dist [0.25].

fffile.txt

Reads the ASCII file ffile.txt and places labels at locations in the file that matches locations along the quoted lines. Inexact matches and points outside the region are skipped.

l|Lline1[,line2,…]

Give the coordinates of the end points for one or more comma-separated straight line segments. Labels will be placed where these lines intersect the quoted lines. The format of each line specification is start_lon/start_lat/stop_lon/stop_lat. Both start_lon/start_lat and stop_lon/stop_lat can be replaced by a 2-character key that uses the justification format employed in text to indicate a point on the frame or center of the map, given as [LCR][BMT]. L will interpret the point pairs as defining great circles [Default is straight line].

n|Nn_label

Specifies the number of equidistant labels for quoted lines [1]. Upper case N starts labeling exactly at the start of the line [Default centers them along the line]. N-1 places one justified label at start, while N+1 places one justified label at the end of quoted lines. Optionally, append /min_dist[c|i|p] to enforce that a minimum distance separation between successive labels is enforced.

s|Sn_label

Same as n|Nn_label but implies that the input data are first to be converted into a series of 2-point line segments before plotting.

x|Xxfile.txt

Reads the multisegment file xfile.txt and places labels at the intersections between the quoted lines and the lines in xfile.txt. X will resample the lines first along great-circle arcs. In addition, you may optionally append +rradius[c|i|p] to set a minimum label separation in the x-y plane [no limitation].

The optional labelinfo controls the specifics of the label formatting and consists of a concatenated string made up of any of the following control arguments:

+aangle

For annotations at a fixed angle, +an for line-normal, or +ap for line-parallel [Default].

+cdx[/dy]

Sets the clearance between label and optional text box. Append c|i|p to specify the unit or % to indicate a percentage of the label font size [15%].

+d

Turns on debug which will draw helper points and lines to illustrate the workings of the quoted line setup.

+e

Delay the plotting of the text. This is used to build a clip path based on the text, then lay down other overlays while that clip path is in effect, then turning of clipping with clip -Cs which finally plots the original text.

+ffont

Sets the desired font [Default FONT_ANNOT_PRIMARY with its size changed to 9p].

+g[color]

Selects opaque text boxes [Default is transparent]; optionally specify the color [Default is PS_PAGE_COLOR].

+jjust

Sets label justification [Default is MC]. Ignored when -SqN|n+|-1 is used.

+llabel

Sets the constant label text. Warning: if the text length exceeds the line length then no text will appear.

+Lflag

Sets the label text according to the specified flag:

+Lh Take the label from the current segment header (first scan for an embedded -Llabel option, if not use the first word following the segment flag). For multiple-word labels, enclose entire label in double quotes. +Ld Take the Cartesian plot distances along the line as the label; append c|i|p as the unit [Default is PROJ_LENGTH_UNIT]. +LD Calculate actual map distances; append d|e|f|k|n|M|n|s as the unit [Default is d(egrees), unless label placement was based on map distances along the lines in which case we use the same unit specified for that algorithm]. Requires a map projection to be used. +Lf Use text after the 2nd column in the fixed label location file as the label. Requires the fixed label location setting. +Lx As +Lh but use the headers in the xfile.txt instead. Requires the crossing file option.

+ndx[/dy]

Nudges the placement of labels by the specified amount (append c|i|p to specify the units). Increments are considered in the coordinate system defined by the orientation of the line; use +N to force increments in the plot x/y coordinates system [no nudging]. Not allowed with +v.

+o

Selects rounded rectangular text box [Default is rectangular]. Not applicable for curved text (+v) and only makes sense for opaque text boxes.

+p[pen]

Draws the outline of text boxes [Default is no outline]; optionally specify pen for outline [Default is width = 0.25p, color = black, style = solid].

+rmin_rad

Will not place labels where the line’s radius of curvature is less than min_rad [Default is 0].

+t[file]

Saves line label x, y, and text to file [Line_labels.txt]. Use +T to save x, y, angle, text instead.

+uunit

Appends unit to all line labels. If unit starts with a leading hyphen (-) then there will be no space between label value and the unit. [Default is no unit].

+v

Specifies curved labels following the path [Default is straight labels].

+w

Specifies how many (x,y) points will be used to estimate label angles [Default is 10].

+x[first,last]

Append the suffices first and last to the corresponding labels.

This modifier is only available when -SqN2 is in effect. Used to annotate the start and end of a line (e.g., a cross-section), append two text strings separated by comma [Default just adds a prime to the second label].

+=prefix

Prepends prefix to all line labels. If prefix starts with a leading hyphen (-) then there will be no space between label value and the prefix. [Default is no prefix].

Note: By placing -Sq options in the segment header you can change the quoted text attributes on a segment-by-segment basis.

-Sr

rectangle. No size needs to be specified, but the x- and y-dimensions must be found in columns 3 and 4. Alternatively, append +s and then the diagonal corner coordinates are expected in columns 3 and 4.

-SR

Rounded rectangle. No size needs to be specified, but the x- and y-dimensions and corner radius must be found in columns 3, 4, and 5.

-Ss

square. size is diameter of circumscribing circle.

-St

triangle. size is diameter of circumscribing circle.

-Sv

vector. Direction (in degrees counter-clockwise from horizontal) and length must be found in columns 3 and 4, and size, if not specified on the command-line, should be present in column 5. The size is the length of the vector head. Vector stem width is set by -W, with head outline pen width defaulting to half of stem pen width. See Vector Attributes for specifying this and other attributes. But also be aware that using color via a CPT implies a shift of columns 3 and on to accommodate the color fill determined by the z-value in new 3rd column (See -C option).

-SV

Same as -Sv, except azimuth (in degrees east of north) should be given instead of direction. The azimuth will be mapped into an angle based on the chosen map projection (-Sv leaves the directions unchanged.) If your length is not in plot units but in arbitrary user units (e.g., a rate in mm/yr) then you can use the -i option to scale the corresponding column via the +sscale modifier. See Vector Attributes for specifying symbol attributes.

-Sw

pie wedge. Start and stop directions (in degrees counter-clockwise from horizontal) for pie slice must be found in columns 3 and 4. Append /inner to select a separate inner diameter [0]. Append +a[dr] to draw the arc line (at inner and outer diameter); if dr is appended then we draw all arc lines separated radially by dr. Append +r[da] to draw radial lines (at start and stop directions) if da is appended then we draw all radial lines separated angularly by da. These spider-web lines are drawn using the current pen unless +ppen is added.

-SW

Same as -Sw, except azimuths (in degrees east of north) should be given instead of the two directions. The azimuths will be mapped into angles based on the chosen map projection (-Sw leaves the directions unchanged). Specify size as a geographical diameter. For allowable geographical units, see Units [Default is k for km]. To instead specify a diameter in plot units, you must append the desired unit. Append /inner to select a separate inner diameter [0]. Append +a[dr] to draw the arc line (at inner and outer diameter); if dr is appended then we draw all arc lines separated radially by dr. Append +r[da] to draw radial lines (at start and stop directions) if da is appended then we draw all radial lines separated angularly by da. These spider-web lines are drawn using the current pen unless +ppen is added.

-Sx

cross (x). size is diameter of circumscribing circle.

-Sy

y-dash (|). size is the length of a short vertical (y-dir) line segment.

-S=

geovector. Azimuth (in degrees east from north) and geographical length must be found in columns 3 and 4. The size is the length of the vector head. Vector width is set by -W. See Vector Attributes for specifying attributes. Note: Geovector stems are drawn as thin filled polygons and hence pen attributes like dashed and dotted are not available. For allowable geographical units, see Units.

-S~

decorated line, i.e., lines with symbols along them. Append [d|D|f|l|L|n|N|s|S|x|X]info[:symbolinfo]. The required argument controls the placement of symbols along the decorated lines. Choose among six controlling algorithms:

ddist[c|i|p] or Ddist[d|e|f|k|m|M|n|s]

For lower case d, give distances between symbols on the plot in your preferred measurement unit c (cm), i (inch), or p (points), while for upper case D, specify distances in map units and append the unit; choose among e (m), f (foot), k (km), M (mile), n (nautical mile) or u (US survey foot), and d (arc degree), m (arc minute), or s (arc second). [Default is 10c or 4i]. As an option, you can append /fraction which is used to place the very first symbol for each line when the cumulative along-line distance equals fraction * dist [0.25].

fffile.txt

Reads the ASCII file ffile.txt and places symbols at locations in the file that matches locations along the decorated lines. Inexact matches and points outside the region are skipped.

l|Lline1[,line2,…]

Give the coordinates of the end points for one or more comma-separated straight line segments. Symbols will be placed where these lines intersect the decorated lines. The format of each line specification is start_lon/start_lat/stop_lon/stop_lat. Both start_lon/start_lat and stop_lon/stop_lat can be replaced by a 2-character key that uses the justification format employed in text to indicate a point on the frame or center of the map, given as [LCR][BMT]. L will interpret the point pairs as defining great circles [Default is straight line].

n|Nn_symbol

Specifies the number of equidistant symbols for decorated lines [1]. Upper case N starts placing symbols exactly at the start of the line [Default centers them along the line]. N-1 places one symbol at start, while N+1 places one symbol at the end of decorated lines. Optionally, append /min_dist[c|i|p] to enforce that a minimum distance separation between successive symbols is enforced.

s|Sn_symbol

Same as n|Nn_symbol but implies that the input data are

first to be converted into a series of 2-point line segments before plotting.

x|Xxfile.txt

Reads the multisegment file xfile.txt and places symbols at the intersections between the decorated lines and the lines in xfile.txt. X will resample the lines first along great-circle arcs.

The optional symbolinfo controls the specifics of the symbol selection and formatting and consists of a concatenated string made up of any of the following control arguments:

+aangle

For symbols at a fixed angle, +an for line-normal, or +ap for line-parallel [Default].

+d

Turns on debug which will draw helper points and lines to illustrate the workings of the decorated line setup.

+g[fill]

Sets the symbol fill [no fill].

+ndx[/dy]

Nudges the placement of symbols by the specified amount (append c|i|p to specify the units). Increments are considered in the coordinate system defined by the orientation of the line; use +N to force increments in the plot x/y coordinates system [no nudging].

+p[pen]

Draws the outline of symbols [Default is no outline]; optionally specify pen for outline [Default is width = 0.25p, color = black, style = solid].

+s<symbol><size>

Specifies the code and size of the decorative symbol.

+w

Specifies how many (x,y) points will be used to estimate symbol angles [Default is 10].

Note: By placing -S~ options in the segment header you can change the decorated lines on a segment-by-segment basis.

-U[label][+c][+jjust][+odx/dy] (more …): Draw GMT time stamp logo on plot.

-V[level] (more …): Select verbosity level [c].

-W[pen][attr] (more …): Set pen attributes for lines or the outline of symbols [Defaults: width = default, color = black, style = solid]. If the modifier +cl is appended then the color of the line are taken from the CPT (see -C). If instead modifier +cf is appended then the color from the cpt file is applied to symbol fill. Use just +c for both effects. You can also append one or more additional line attribute modifiers: +ooffsetu will start and stop drawing the line the given distance offsets from the end point. Append unit u from c|i|p to indicate plot distance on the map or append map distance units instead (see below) [Cartesian distances]; +s will draw the line using a Bezier spline [linear spline]; +vvspecs will place a vector head at the ends of the lines. You can use +vb and +ve to specify separate vector specs at each end [shared specs]. Because +v may take additional modifiers it must necessarily be given at the end of the pen specification. See the Vector Attributes for more information.

-X[a|c|f|r][xshift[u]]

-Y[a|c|f|r][yshift[u]] (more …): Shift plot origin.

-Z[l|f]value: Instead of specifying a symbol or polygon fill and outline color via -G and -W, give both a level value via -Z and a color lookup table via -C. To just set the fill or outline, use -Zf or -Zl, respectively.

-bi[ncols][t] (more …): Select native binary format for primary input. [Default is the required number of columns given the chosen settings].

-acol=name[…] (more …): Set aspatial column associations col=name.

-dinodata (more …): Replace input columns that equal nodata with NaN.

-e[~]”pattern” | -e[~]/regexp/[i] (more …): Only accept data records that match the given pattern.

-f[i|o]colinfo (more …): Specify data types of input and/or output columns.

-g[a]x|y|d|X|Y|D|[col]zgap[u][+n|p] (more …): Determine data gaps and line breaks. The -g option is ignored if -S is set.

-h[i|o][n][+c][+d][+rremark][+rtitle] (more …): Skip or produce header record(s).

-icols[+l][+sscale][+ooffset][,…][,t[word]] (more …): Select input columns and transformations (0 is first column, t is trailing text, append word to read one word only).

-l[label][+dpen][+ffont][+ggap][+hheader][+jjust][+l[code/]txt][+ncols][+ssize][+v[pen]][+wwidth][+xscale] (more …): Add a legend entry for the symbol or line being plotted.

-:[i|o] (more …): Swap 1st and 2nd column on input and/or output.

-p[x|y|z]azim[/elev[/zlevel]][+wlon0/lat0[/z0]][+vx0/y0] (more …): Select perspective view.

-t[transp] (more …): Set transparency level in percent.

If no transparency is appended then we will read it from the last column per data record instead.

-^ or just -: Print a short message about the syntax of the command, then exits (NOTE: on Windows just use -).
-+ or just +: Print an extensive usage (help) message, including the explanation of any module-specific option (but not the GMT common options), then exits.
-? or no arguments: Print a complete usage (help) message, including the explanation of all options, then exits.
--PAR=value: Temporarily override a GMT default setting; repeatable. See gmt.conf for parameters.

Units¶

For map distance unit, append unit d for arc degree, m for arc minute, and s for arc second, or e for meter [Default], f for foot, k for km, M for statute mile, n for nautical mile, and u for US survey foot. By default we compute such distances using a spherical approximation with great circles (-jg) using the authalic radius (see PROJ_MEAN_RADIUS). You can use -jf to perform “Flat Earth” calculations (quicker but less accurate) or -je to perform exact geodesic calculations (slower but more accurate; see PROJ_GEODESIC for method used).

Vector Attributes¶

Several modifiers may be appended to vector-producing options for specifying the placement of vector heads, their shapes, and the justification of the vector. Below, left and right refers to the side of the vector line when viewed from the start point to the end point of a segment:

+aangle sets the angle of the vector head apex [30].

+b places a vector head at the beginning of the vector path [none]. Optionally, append t for a terminal line, c for a circle, a for arrow [Default], i for tail, A for plain open arrow, and I for plain open tail. Further append l|r to only draw the left or right half-sides of this head [both sides].

+e places a vector head at the end of the vector path [none]. Optionally, append t for a terminal line, c for a circle, a for arrow [Default], i for tail, A for plain open arrow, and I for plain open tail. Further append l|r to only draw the left or right half-sides of this head [both sides].

+g[fill*] sets the vector head fill [Default fill is used, which may be no fill]. Turn off vector head fill by not appending a fill.

+hshape sets the shape of the vector head (range -2/2). Default is controlled by MAP_VECTOR_SHAPE [0].

+l draws half-arrows, using only the left side of specified heads [both sides].

+m places a vector head at the mid-point the vector path [none]. Append f or r for forward or reverse direction of the vector [forward]. Optionally, append t for a terminal line, c for a circle, a for arrow [Default], i for tail, A for plain open arrow, and I for plain open tail. Further append l|r to only draw the left or right half-sides of this head [both sides]. Cannot be combined with +b or +e.

+nnorm scales down vector attributes (pen thickness, head size) with decreasing length, where vector plot lengths shorter than norm will have their attributes scaled by length/norm [arrow attributes remains invariant to length]. For Cartesian vectors specify a length in plot units, while for geovectors specify a length in km.

+o[plon/plat] specifies the oblique pole for the great or small circles. Only needed for great circles if +q is given. If no pole is appended then we default to the north pole.

+p[pen] sets the vector pen attributes. If no pen is appended then the head outline is not drawn. [Default pen is half the width of stem pen, and head outline is drawn]

+q means the input angle, length data instead represent the start and stop opening angles of the arc segment relative to the given point. See +o to specify a specific pole for the arc [north pole].

+r draws half-arrows, using only the right side of specified heads [both sides].

+t[b|e]trim[unit] will shift the beginning or end point (or both) along the vector segment by the given trim; append suitable unit (c, i, or p). If the modifiers b|e are not used then trim may be two values separated by a slash, which is used to specify different trims for the beginning and end. Positive trims will shorted the vector while negative trims will lengthen it [no trim].

In addition, all but circular vectors may take these modifiers:

+jjust determines how the input x,y point relates to the vector. Choose from beginning [default], end, or center.

+s means the input angle, length are instead the x, y coordinates of the vector end point.

Finally, Cartesian vectors may take these modifiers:

+zscale[unit] expects input dx,dy vector components and uses the scale to convert to polar coordinates with length in given unit.

Note: Vectors were completely redesigned for GMT5 which separated the vector head (a polygon) from the vector stem (a line). In GMT4, the entire vector was a polygon and it could only be a straight Cartesian vector. Yes, the old GMT4 vector shape remains accessible if you specify a vector (-Sv|V) using the GMT4 syntax, explained here: size, if present, will be interpreted as arrowwidth/headlength/headwidth [Default is 0.075c/0.3c/0.25c (or 0.03i/0.12i/0.1i)]. By default, arrow attributes remain invariant to the length of the arrow. To have the size of the vector scale down with decreasing size, append nnorm, where vectors shorter than norm will have their attributes scaled by length/norm. To center the vector on the balance point, use −Svb; to align point with the vector head, use −Svh; to align point with the vector tail, use −Svt [Default]. To give the head point’s coordinates instead of direction and length, use −Svs. Upper case B, H, T, S will draw a double-headed vector [Default is single head].

Examples¶

Note: Below are some examples of valid syntax for this module. The examples that use remote files (file names starting with @) can be cut and pasted into your terminal for testing. Other commands requiring input files are just dummy examples of the types of uses that are common but cannot be run verbatim as written.

Note: Since many GMT plot examples are very short (i.e., one module call between the gmt begin and gmt end commands), we will often present them using the quick modern mode GMT Modern Mode One-line Commands syntax, which simplifies such short scripts.

To plot solid red circles (diameter = 0.2 cm) at the positions listed in the remote file DSDP.txt on a Mercator map at 0.3 cm/degree of the area 100E to 160E, 20S to 30N, with automatic tick-marks and gridlines, use

gmt plot @DSDP.txt -R100/160/-20/30 -Jm0.3c -Sc0.2c -Gred -Bafg -pdf map

To plot the xyz values in the file quakes.xyzm as circles with size given by the magnitude in the 4th column and color based on the depth in the third using the CPT rgb.cpt on a linear map, use

gmt plot quakes.xyzm -R0/1000/0/1000 -JX6i -Sc -Crgb -B200 -pdf map

To plot the file trench.txt on a Mercator map, with white triangles with sides 0.25 inch on the left side of the line, spaced every 0.8 inch, use

gmt plot trench.txt -R150/200/20/50 -Jm0.15i -Sf0.8i/0.1i+l+t -Gwhite -W -B10 -pdf map

To plot a point with color dictated by the t.cpt file for the z-value 65, try

echo 175 30 | gmt plot -R150/200/20/50 -JM15c -Sc0.5c -Zf65 -Ct.cpt -pdf map

To plot the data in the file misc.txt as symbols determined by the code in the last column, and with size given by the magnitude in the 4th column, and color based on the third column via the CPT chrome on a linear map, use

gmt plot misc.txt -R0/100/-50/100 -JX6i -S -Cchrome -B20 -pdf map

If you need to place vectors on a plot you can choose among straight Cartesian vectors, math circular vectors, or geo-vectors (these form small or great circles on the Earth). These can have optional heads at either end, and heads may be the traditional arrow, a circle, or a terminal cross-line. To place a few vectors with a circle at the start location and an arrow head at the end, try

gmt plot -R0/50/-50/50 -JX6i -Sv0.15i+bc+ea -Gyellow -W0.5p -Baf -pdf map << EOF
10 10 45 2i
30 -20 0 1.5i
EOF

To plot vectors (red vector heads, solid stem) from the file data.txt that contains record of the form lon, lat, dx, dy, where dx, dy are the Cartesian vector components given in user units, and these user units should be converted to cm given the scale 3.60, try

gmt plot -R20/40/-20/0 -JM6i -Sv0.15i+e+z3.6c -Gred -W0.25p -Baf data.txt -pdf map

Segment Header Parsing¶

Segment header records may contain one of more of the following options:

-Gfill: Use the new fill and turn filling on
-G-: Turn filling off
-G: Revert to default fill (none if not set on command line)
-Wpen: Use the new pen and turn outline on
-W: Revert to default pen MAP_DEFAULT_PEN (if not set on command line)
-W-: Turn outline off
-Zzval: Obtain fill via cpt lookup using z-value zval
-ZNaN: Get the NaN color from the CPT

Custom Symbols¶

GMT allows users to define and plot their own custom symbols. This is done by encoding the symbol using our custom symbol macro code described in Appendix N. Put all the macro codes for your new symbol in a file whose extension must be .def; you may then address the symbol without giving the extension (e.g., the symbol file tsunami.def is used by specifying -Sktsunami/size. The definition file can contain any number of plot code records, as well as blank lines and comment lines (starting with #). The module will look for the definition files in (1) the current directory, (2) the ~/.gmt directory, and (3) the $GMT_SHAREDIR/custom directory, in that order. Freeform polygons (made up of straight line segments and arcs of circles) can be designed - these polygons can be painted and filled with a pattern. Other standard geometric symbols can also be used. See Appendix Custom Plot Symbols for macro definitions.

GMT4 Vector¶

Note: The old-style, single-polygon vector available in GMT4 and earlier versions has been added to GMT5 for backwards compatibility with old scripts. For reference, the old vector syntax is listed here: The size, if present, will be interpreted as arrowwidth/headlength/headwidth. By default, arrow attributes remain invariant to the length of the arrow. To have the size of the vector scale down with decreasing length, append nnorm, so that vectors shorter than norm will have their dimensions scaled by the vector length divided by norm. To center the vector on the balance (mid) point, use -Svb; to align point with the vector head, use -Svh; to align point with the vector tail, use -Svt [Default]. If the input has the head point’s coordinates instead of direction and length, use -Svs. Upper case B, H, T, or S will draw a double-headed vector [Default is single head].

Polar Caps¶

We will automatically determine if a closed polygon is containing a geographic pole, i.e., being a polar cap. Such polygons requires special treatment under the hood to ensure proper filling. Many tools such as GIS packages are unable to handle polygons covering a pole and some cannot handle polygons crossing the Dateline. They work around this problem by splitting polygons into a west and east polygon or inserting artificial helper lines that makes a cut into the pole and back. Such doctored polygons may be misrepresented in GMT.