👍 - it'd be useful to put a docstring on the class, just to clarify that this is only defined over the US (sadly, as the rendering is beautiful).

I certainly think we can streamline the construction of some of these services - I'm not too worried about doing that in this PR, but please feel free to investigate as a follow on.

There are a few PEP8 test failiures from this PR:

test_pep8_conformance (cartopy.tests.test_pep8.TestCodeFormat) ... /usr/local/lib/python2.7/dist-packages/cartopy/io/img_tiles.py:226:1: W293 blank line contains whitespace
/usr/local/lib/python2.7/dist-packages/cartopy/io/img_tiles.py:227:1: E302 expected 2 blank lines, found 1
/usr/local/lib/python2.7/dist-packages/cartopy/io/img_tiles.py:232:80: E501 line too long (82 > 79 characters)
/usr/local/lib/python2.7/dist-packages/cartopy/io/img_tiles.py:235:1: E302 expected 2 blank lines, found 1

Okay, updated for PEP8 compliance and added a docstring describing this US coverage. Note that the tools for creating these tiles are at https://github.com/migurski/DEM-Tools and at least the Canadians have used them: migurski/DEM-Tools#4
The lower zoom levels are from SRTM worldwide coverages (coverages: NED10m, NED100m, NED1km, SRTM1, SRTM3)

Should we call this OSMTerrain or USTerrain instead of StamenTerrain?

Are there python editors that test pep8 compliance? It seems like using Travis CI to find pep8 errors is a bit of a waste...

@pelson, So I see that this PR still fails, but is this something I need to fix?

======================================================================
FAIL: cartopy.tests.mpl.test_images.test_web_tiles
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/usr/local/lib/python2.7/dist-packages/nose/util.py", line 618, in newfunc
    return func(*arg, **kw)
  File "/usr/local/lib/python2.7/dist-packages/cartopy/tests/mpl/__init__.py", line 210, in wrapped
    self.run_figure_comparisons(figures, test_name=mod_name)
  File "/usr/local/lib/python2.7/dist-packages/cartopy/tests/mpl/__init__.py", line 150, in run_figure_comparisons
    self.do_compare(result_path, expected_path, self.tolerance)
  File "/usr/local/lib/python2.7/dist-packages/cartopy/tests/mpl/__init__.py", line 184, in do_compare
    assert False, msg
AssertionError: Images were different (RMS: 1.80599137902).
/home/travis/build/SciTools/test_folder/cartopy_test_output/test_images/result-web_tiles.png /usr/local/lib/python2.7/dist-packages/cartopy/tests/mpl/baseline_images/mpl/test_images/web_tiles.png /home/travis/build/SciTools/test_folder/cartopy_test_output/test_images/result-web_tiles-failed-diff.png
Consider running idiff to inspect these differences.

The local tests you run before submitting your PR should pick up the PEP8 errors so you can get them cleared up before you push your branch.

You can also run pep8 yourself (pip install pep8 or similar) and then pep8 filename.py which will check the whole file (fine if it was already PEP8 compliant and you made changes) or

git diff -U0 upstream/master | pep8 --diff

to just check the lines you changed relative to the upstream master branch.

You can configure many editors to do PEP8 checking, I generally don't bother and instead rely on the locally run test suite and/or manual checking, but that is personal preference.

So I see that this PR still fails, but is this something I need to fix?

I think the Google tiles have changed (ocean names have moved position) since the static image was created. I don't believe this is due to your code so you are safe to ignore it.

Thanks for the tutorage, @ajdawson !

so okay to merge?

Is the "build.out" file supposed to be included?

Thanks @rsignell-usgs - I've rebased and squashed these onto master as 727d0ed. (I've assumed "build.out" was just a mistake so it's not included.)