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.. _geography:
Drawing a Map Background
========================
Basemap includes the `GSHHG <https://www.soest.hawaii.edu/pwessel/gshhg/>`_
coastline dataset, as well as datasets for rivers, state and
country boundaries from
`GMT <https://www.generic-mapping-tools.org/>`_.
These datasets can be used to draw coastlines, rivers and political
boundaries on maps at several different resolutions. The relevant Basemap
methods are:
* :func:`~mpl_toolkits.basemap.Basemap.drawcoastlines`: draw coastlines.
* :func:`~mpl_toolkits.basemap.Basemap.fillcontinents`: color the interior
of continents (by filling the coastline polygons).
Unfortunately, the fillcontinents method doesn't always do the right thing.
Matplotlib always tries to fill the inside of a polygon. Under certain situations,
what is the inside of a coastline polygon can be ambiguous, and the
outside may be filled instead of the inside.
In these situations, the recommended workaround is to use the
:func:`~mpl_toolkits.basemap.Basemap.drawlsmask` method to
overlay an image with different colors specified for land and water regions
(see below).
* :func:`~mpl_toolkits.basemap.Basemap.drawcountries`: draw country boundaries.
* :func:`~mpl_toolkits.basemap.Basemap.drawstates`: draw state boundaries
in North America.
* :func:`~mpl_toolkits.basemap.Basemap.drawrivers`: draw rivers.
Instead of drawing coastlines and political boundaries, an image can be
used as a map background. Basemap provides several options for this:
* :func:`~mpl_toolkits.basemap.Basemap.drawlsmask`: draw a high-resolution
land-sea mask as an image, with land and ocean colors specified. The land-sea
mask is derived from the GSHHS coastline data, and there are several
coastline options and pixel sizes to choose from.
* :func:`~mpl_toolkits.basemap.Basemap.bluemarble`: draw a NASA
`Blue Marble <https://visibleearth.nasa.gov/images/73726/june-blue-marble-next-generation-w-topography-and-bathymetry>`_
image as a map background.
* :func:`~mpl_toolkits.basemap.Basemap.shadedrelief`: draw a
`shaded relief <https://www.shadedrelief.com/>`_ image
as a map background.
* :func:`~mpl_toolkits.basemap.Basemap.etopo`: draw an
`etopo <https://www.ngdc.noaa.gov/mgg/global/global.html>`_
relief image as map background.
* :func:`~mpl_toolkits.basemap.Basemap.warpimage`: use an abitrary
image as a map background. The image must be global, covering the
world in lat/lon coordinates from the international dateline eastward
and the South Pole northward.
Here are examples of the various ways to draw a map background.
1. Draw coastlines, filling ocean and land areas.
.. plot:: source/users/figures/background1.py
2. Draw a land-sea mask as an image.
.. plot:: source/users/figures/background2.py
3. Draw the NASA 'Blue Marble' image.
.. plot:: source/users/figures/background3.py
4. Draw a shaded relief image.
.. plot:: source/users/figures/background4.py
5. Draw an etopo relief image.
.. plot:: source/users/figures/background5.py
|
