better control of GoogleVisibleMap domain about salem

[fmaussion]

Thanks for raising this! The documentation could be more informative indeed.

Are you referring to the fact that the google map doesn't fit exactly the provided extent? If so, I'm afraid there is no simple solution: it is a limitation of the static google maps API which only has a finite number of zoom levels. GoogleVisibleMap chooses the highest zoom level guaranteed to cover the provided extent.

The simplest workaround (but requiring trial and error) is to play with the size_* kwarg:

from salem import GoogleVisibleMap, Map
import matplotlib.pyplot as plt

mapextent = [-82, -65, 17, 31] # W, E, S, N

g = GoogleVisibleMap(x=[mapextent[0], mapextent[1]], y=[mapextent[2], mapextent[3]],
                     scale=2,  # this provides a higher resolution ggl image but takes longer to download
                     size_x=200, size_y=200,  # this makes the map smaller starting from its centre
                    )
ggl_img = g.get_vardata()

fig, ax = plt.subplots(1, 1, figsize=(12,8))
sm = Map(g.grid, factor=1)  # factor=1 is nicer here because it prevents image resizing
sm.set_rgb(ggl_img)
sm.visualize(ax=ax)

Another possibility would be to add an "ExactGoogleVisibleMap" which would do this size_* picking for us. I can consider adding this to salem, but it might not be trivial.