▦ Gridlines

How to add grid lines to a map

Gridlines can be added to the map via Maps.add_gridlines().

If d is provided, the gridlines will be fixed

• If you provide a number, it is used as grid-spcing (in degrees)

• If you provide a list or numpy.array, it is used to draw lines only at the specific coordinates

• To use different settings for latitude and longitude lines, provide a 2-tuple of the aforementioned types.

If no explicit grid-spacing is provided (e.g. d=None), the grid is dynamically updated based on the visible extent.

• Use auto_n=... to adjust the density of the auto-gridlines.

Maps.add_gridlines

Add gridlines to the map.

Maps.add_gridlines

Add gridlines to the map.

from eomaps import Maps
m = Maps(Maps.CRS.Mollweide(), frameon=False)
m.add_feature.preset.ocean()

# add gridlines with a fixed grid-spacing
mg = m.new_layer("grid")
g0 = mg.add_gridlines(d=40, ec="orange", lw=3, zorder=2)
g1 = mg.add_gridlines(d=(10, 20), ec="orange", lw=.5, zorder=1)

# add fine-grained gridlines in a specific area
g2 = mg.add_gridlines(d=2, ec="darkred", lw=0.5, zorder=0,
                      bounds=(-20, 20, -10, 30))
g3 = mg.add_gridlines(d=2, ec="b", lw=0.5, zorder=0,
                      bounds=(60, 100, 30, 70))

# add dedicated gridlines at specific coordinates
g4 = mg.add_gridlines(([-123, -112, -75], [35, 65]),
                      ec="k", lw=2, ls="--", zorder=20,
                      bounds=(-140, 20, -50, 70)
                      )

m.show_layer(m.layer, "grid")

In addition, the returned GridLines instance supports the following useful methods:

GridLines	Base class for EOmaps grid-lines (and associated grid-labels).
GridLines.set_d	Set a fixed gridline distance (in degrees).
GridLines.set_auto_n	Set the number of (auto) gridlines to draw in the currently visible extent.
GridLines.set_n	Set the number of intermediate points to calculate for each gridline.
GridLines.set_bounds	Set the extent of the area in which gridlines are drawn.
GridLines.update_line_props	Set/update the properties of the drawn lines (e.g. color, linewidth etc.).
GridLines.remove	Remove the grid from the map.
GridLines.add_labels	Add labels to the gridlines.

How to add labels to a grid

Labels can be added to a grid via the GridLines.add_labels() directive.

In general, labels are added at points where the lines of the grid intersects with the axis-boundary. (Note that this provides a lot of flexibility since a map can have as many grids as you like and each grid can have its own labels!)

The where parameter can be used to control where grid labels are added:

• Use an arbitrary combination of the letters "tblr" to draw labels at the top, bottom, left or right boundaries.

  • If this option is used, longitude-lines are only labeled top/bottom and latitude-lines are only labeled left/right.

• Use "all" to label all intersection points.

• Use an integer to draw labels only at the nth found intersection-points.

In addition, the exclude parameter can be used to exclude specific labels based on their lon/lat values and the every parameter can be used to add a label only to every n^th grid line.

To change the appearance of the labels, any kwarg supported by matplotlib.pyplot.text can be used (e.g. color, fontsize, fontweight, …).

from eomaps import Maps
m = Maps(Maps.CRS.Stereographic(), figsize=(5, 6))
m.set_extent((-83, -20, -59, 13))
m.add_feature.preset.coastline()
m.add_feature.preset.ocean()

# draw a regular grid with 10 degree grid-spacing
# and add labels to all lines except some selected lines
g = m.add_gridlines(10, lw=0.25, alpha=0.5)
g.add_labels(fontsize=6, exclude=([-40, -30], [-30]))

# draw some specific gridlines and add bold green labels
g = m.add_gridlines(([-40, -30], [-30]), c="g", lw=1.5)
gl0 = g.add_labels(where="tlr", c="g", offset=15, fontweight="bold")

# draw a bounded grid and add labels
g = m.add_gridlines(10, bounds=[-50, -20, -40, -20], c="b", lw=2)
g = m.add_gridlines(5,  bounds=[-50, -20, -40, -20], c="b")
gl = g.add_labels(where=0, fontsize=8, every=(1, -1, 2), c="b")