Note
Click here to download the full example code
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])
Out:
grdblend [NOTICE]: Remote data courtesy of GMT data server oceania [http://oceania.generic-mapping-tools.org]
grdblend [NOTICE]: Earth Relief at 5x5 arc minutes from Gaussian Cartesian filtering (9 km fullwidth) of SRTM15+V2.1 [Tozer et al., 2019].
grdblend [NOTICE]: -> Download 180x180 degree grid tile (earth_relief_05m_p): S90W180
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 1000 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)
Out:
<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 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)
Out:
<IPython.core.display.Image object>
Contour limits
The limit
argument sets the minimum and maximum values for the contour
lines. The argument 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)
Out:
<IPython.core.display.Image object>
Map settings
The pygmt.Figure.grdcontour
method accepts additional arguments,
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)
Out:
<IPython.core.display.Image object>
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
argument is specified in the
pygmt.Figure.grdimage
method, it does not need to be repeated in the
pygmt.Figure.grdcontour
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.show()
![contour map](../_images/sphx_glr_contour_map_005.png)
Out:
<IPython.core.display.Image object>
Total running time of the script: ( 0 minutes 10.693 seconds)