contour_map.py

"""
Creating a map with contour lines
=================================

Plotting a contour map is handled by :meth:`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 :meth:`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 line settings
# ---------------------
#
# Use the ``annotation`` and ``levels`` 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(grid=grid, annotation=1000, levels=250)
fig.show()


# %%
# 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(grid=grid, annotation=1000, levels=250, limit=[-4000, -2000])
fig.show()


# %%
# Map settings
# ------------
#
# The :meth:`pygmt.Figure.grdcontour` method accepts additional parameters, including
# setting the projection and frame.

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


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

fig = pygmt.Figure()
fig.grdimage(grid=grid, cmap="gmt/haxby", projection="M10c", frame=True)
fig.grdcontour(grid=grid, annotation=1000, levels=250, limit=[-4000, -2000])
fig.colorbar(label="Elevation", unit="m")
fig.show()

# sphinx_gallery_thumbnail_number = 5