Creating a map with contour lines

Plotting a contour map is handled by pygmt.Figure.grdcontour

import pygmt

Create contour plot

The grdcontour method takes the grid input and the region values. It plots annotated contour lines, which are darker and have the elevation/depth written on them, and unannotated contour lines. In the example blow, the default contour line intervals are 500 meters, with an annotated contour line every 1000 meters. By default, it plots the map with a Equidistant cylindrical projection and with no frame.

fig = pygmt.Figure()
fig.grdcontour(grid="@earth_relief_15s", region=[-92, -90, -1.5, 0.5])
fig.show()

Out:

grdblend [NOTICE]: Remote data courtesy of GMT data server OCEANIA [https://oceania.generic-mapping-tools.org]
grdblend [NOTICE]: Earth Relief at 15x15 arc seconds provided by SRTM15+V2.1 [Tozer et al., 2019].
grdblend [NOTICE]:   -> Download 10x10 degree grid tile (earth_relief_15s_p): S10W100

<IPython.core.display.Image object>

Contour line settings

Use the “annotation” and “interval” arguments to adjust contour line intervals In the example below, there are contour intervals every 250 meters and an annotated contour line every 1,000 meters.

fig = pygmt.Figure()
fig.grdcontour(
    annotation=1000,
    interval=250,
    grid="@earth_relief_15s",
    region=[-92, -90, -1.5, 0.5],
)
fig.show()

Out:

<IPython.core.display.Image object>

Contour limits

The limit argument sets the minimum and maximum values for the contour lines, with the value. The argument takes the low and high values, and is either a list (as below) or a string limit=”-4000/0”

fig = pygmt.Figure()
fig.grdcontour(
    annotation=1000,
    interval=250,
    grid="@earth_relief_15s",
    region=[-92, -90, -1.5, 0.5],
    limit=[-4000, 0],
)
fig.show()

Out:

<IPython.core.display.Image object>

Map settings

The grdcontour method accepts additional arguments, including setting the projection and frame.

fig = pygmt.Figure()
fig.grdcontour(
    annotation=1000,
    interval=250,
    grid="@earth_relief_15s",
    region=[-92, -90, -1.5, 0.5],
    limit=[-4000, 0],
    projection="M4i",
    frame=True,
)
fig.show()

Out:

<IPython.core.display.Image object>