Creating a map with contour lines

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

import pygmt

# Load sample earth relief data
grid = pygmt.datasets.load_earth_relief(resolution="05m", region=[-92.5, -82.5, -3, 7])

Create contour plot

The pygmt.Figure.grdcontour method takes the grid input. It plots annotated contour lines, which are thicker and have the elevation/depth written on them, and unannotated contour lines. In the example below, the default contour line intervals are 500 meters, with an annotated contour line every 1,000 meters. By default, it plots the map with the equidistant cylindrical projection and with no frame.

fig = pygmt.Figure()
fig.grdcontour(grid=grid)
fig.show()

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Contour line settings

Use the annotation and interval parameters to adjust contour line intervals. In the example below, there are contour intervals every 250 meters and annotated contour lines every 1,000 meters.

fig = pygmt.Figure()
fig.grdcontour(
    annotation=1000,
    interval=250,
    grid=grid,
)
fig.show()

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Contour limits

The limit parameter sets the minimum and maximum values for the contour lines. The parameter takes the low and high values, and is either a list (as below) or a string limit="-4000/-2000".

fig = pygmt.Figure()
fig.grdcontour(
    annotation=1000,
    interval=250,
    grid=grid,
    limit=[-4000, -2000],
)
fig.show()

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Map settings

The pygmt.Figure.grdcontour method accepts additional parameters, including setting the projection and frame.

fig = pygmt.Figure()
fig.grdcontour(
    annotation=1000,
    interval=250,
    grid=grid,
    limit=[-4000, -2000],
    projection="M10c",
    frame=True,
)
fig.show()

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Adding a colormap

The pygmt.Figure.grdimage method can be used to add a colormap to the contour map. It must be called prior to pygmt.Figure.grdcontour to keep the contour lines visible on the final map. If the projection parameter is specified in the pygmt.Figure.grdimage method, it does not need to be repeated in the pygmt.Figure.grdcontour method. Finally, a colorbar is added using the pygmt.Figure.colorbar method.

fig = pygmt.Figure()
fig.grdimage(
    grid=grid,
    cmap="haxby",
    projection="M10c",
    frame=True,
)
fig.grdcontour(
    annotation=1000,
    interval=250,
    grid=grid,
    limit=[-4000, -2000],
)
fig.colorbar(frame=["x+lelevation", "y+lm"])
fig.show()

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