Buffer polygon

[j-t-t]

Cambridge's city polygon via open street maps is incorrect, leaving out 3% of crashes, most of which are at a high crash intersection. This change intends to correct that, by doing the following for cities that have a polygon

• Look at the crashes for that city. If between 1% and 10% of the crashes fall outside of the city polygon, then try to buffer the city to cover them:
• For any point that falls within 250 m of the city polygon: draw a line between the crash and the nearest point of the polygon. Create a 20 m buffer around the line, and add that buffer to the polygon.
• If the city shape changes at all, use the resulting shape file via graph_from_polygon instead of graph_from_place

For cities that don't have a polygon, results are unchanged. For Boston and DC, fewer than 1% of crashes fall outside the city polygon, so their results are unchanged. For a city whose crash data is for a larger area (say on the county level), more than 10% of crashes would fall outside the city polygon, so that would also remain unchanged. So far, this only affects Cambridge (and will affect neighboring Somerville once Somerville is onboarded).

[codecov[bot]]

Codecov Report

Merging #168 into master will increase coverage by 0.71%. The diff coverage is 77.77%.

@@            Coverage Diff             @@
##           master     #168      +/-   ##
==========================================
+ Coverage   39.93%   40.64%   +0.71%     
==========================================
  Files          26       26              
  Lines        2677     2721      +44     
==========================================
+ Hits         1069     1106      +37     
- Misses       1608     1615       +7