Note
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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()
![contour map](../../_images/sphx_glr_contour_map_001.png)
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()
![contour map](../../_images/sphx_glr_contour_map_002.png)
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()
![contour map](../../_images/sphx_glr_contour_map_003.png)
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()
![contour map](../../_images/sphx_glr_contour_map_004.png)
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()
![contour map](../../_images/sphx_glr_contour_map_005.png)
Total running time of the script: (0 minutes 1.454 seconds)