Updated fillstates.py to add Alaska and Hawaii as map insets #366
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I love this in theory 'cause I forgot too late I left out states, but is there anyway to refine this example so it's not quite this complicated? |
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I thought about it and I don't think the code can be simplified much while maintaining the look of the map. I added three elements: Each of the three elements are essential to a scientifically complete map, and the codes I wrote for each of the three elements are already quite simple. Also, for (1) and (2), I choose to use Mercator projection, because (a) this projection makes Alaska look "upright" instead of "tilted", and (b) enables me to draw straight gray lines on the map. |
examples/fillstates.py
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| m_.plot(np.linspace(-175,-171),np.linspace(26,22),linewidth=1., | ||
| color=light_gray,latlon=True) | ||
| m_.plot(np.linspace(-171,-171),np.linspace(22,20),linewidth=1., | ||
| color=light_gray,latlon=True) |
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These plot commands are distracting and largely overkill anyway. The linspace() doesn't really make sense since all you need are the vertexes. This could be simplified into two plot() calls, or possibly even two Polygons with 'none' as their facecolor?
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I modified these lines into four lines.
However, there is a tiny difference between the new result and old result: the light gray lines in the new version are now slightly thicker and look more "blurred" than the old version...
| #%% --------- Show color bar --------------------------------------- | ||
| ax_c = fig.add_axes([0.9, 0.1, 0.03, 0.8]) | ||
| cb = ColorbarBase(ax_c,cmap=cmap,norm=norm,orientation='vertical', | ||
| label=r'[population per $\mathregular{km^2}$]') |
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Why not a regular colorbar creation approach instead of manually creating axes and such? An example like this is already getting pretty complicated, so we should aim to reduce complexity where-ever possible.
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I tried the regular m.colorbar() way, but I couldn't figure out what I should use for mappable. Please provide advice if you can. Thanks.
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Hi @jsh9:
I have this file around where I was coloring countries based on population. I used it for teaching purposes, so there is an intentional bug somewhere, but you can check out how I did the colorbar there at the end:
https://github.com/guziy/CMOS-python-tutorial/blob/master/fiona_test.py
Cheers
examples/fillstates.py
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| seg = list(map(lambda (x,y): (x-1900000, y+250000), seg)) | ||
| color = rgb2hex(colors[statenames[nshape]]) | ||
| elif shapedict['NAME'] == 'Alaska' and float(shapedict['AREA']) > AREA_2: | ||
| seg = list(map(lambda (x,y): (AK_SCALE*x-200000, AK_SCALE*y-650000), seg)) |
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Why not a list comprehension? Might be easier to read.
Also, could you include a comment to explain how these numbers came about (so that others could adapt this process for other projections, perhaps)?
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Yeah, I will change them to list comprehension. I copied and pasted the list(map(lambda())) directly from here https://stackoverflow.com/questions/39742305/how-to-use-basemap-python-to-plot-us-with-50-states without much thinking
These number are achieved by trial and error; I will add comments to point this out.
| #%% --------- draw state boundaries ---------------------------------------- | ||
| ## data from U.S Census Bureau | ||
| ## http://www.census.gov/geo/www/cob/st2000.html | ||
| shp_info = m.readshapefile('st99_d00','states',drawbounds=True, |
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can this be read in only once and the drawbounds be a part of drawing the polygons?
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Not really. Alaska and Hawaii are plotted using Mercator projection, while the other contiguous states are plotted using Lambert projection. The reason for choosing Mercator projection to plot Alaska and Hawaii is purely an aesthetic one, and I have noticed that this map-making choice (i.e., Alaska and Hawaii being plotted by Mercator projection) was adopted from as early as half a century ago.
I am not sure what you meant by "drawbounds be a part of drawing the polygons". Line 20 is in the original example script.
examples/fillstates.py
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| # cycle through state names, color each one. | ||
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| #%% --------- cycle through state names, color each one. -------------------- | ||
| fig = plt.gcf() # get current figure instance |
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fig, ax = plt.subplots() at the top and then pass the ax kwarg to the Basemap methods?
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The original example script has ax = plt.gca() on that location, and I just added fig = plt.gcf() on top of it because I wanted the changed to the original script to be minimal.
I can change it to what you suggested. It is indeed more elegant.
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Made a new commit just now. Suggestions welcome! |
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Sorry this sat for so long! Hurricane season distracted me and I forgot to get back to this. Thanks for your contribution! |
I modified the example so that the map output imitates the map shown here (basically, Alaska and Hawaii are shown on the bottom left corner of the main map as small insets): https://en.wikipedia.org/wiki/List_of_U.S._states_by_population_density
I based my modifications partly on some code snippets in this stackoverflow thread (https://stackoverflow.com/questions/39742305/how-to-use-basemap-python-to-plot-us-with-50-states).