Posts from — March 2009

Without the quadrant designation, several intersections in Washington–“6th and C,” for example–are ambiguous. “6th and C” can refer to a place in NW, NE, SW, or SE DC. Because of this duplication of streets and intersections, the quadrant is usually–but not always–specified. I’ve been curious  for some time to know exactly how many doubly-, triply-, and quadruply-redundant intersections there are in DC, and it’s another fun example combining Mathematica 7‘s .shp file import with the GIS data that the DC government makes available.

How many are there? I calculate:

The 28 intersections that appear in all 4 quadrants are:

14th & D, 9th & G, 7th & I, 7th & E, 7th & G, 7th & D, 6th & C, 6th & G, 6th & D, 6th & I, 6th & E, 4th & M, 4th & G, 4th & E, 4th & D, 4th & I, 3rd & M, 3rd & C, 3rd & K, 3rd & D, 3rd & G, 3rd & E, 3rd & I, 2nd & E, 2nd & C, 1st & M, 1st & C, 1st & N

Plotted on a map:

Color coded map of intersections in DC.

Update: Here’s a larger PDF version.

Here’s how I made the map and did the calculations:

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