Explained by Elizabeth Pisani:

On this fantastic map, which comes from Yale University’s Dr. Russell Barbour by way of Stop the Drug War, the red areas are the parts of town where it would be illegal to operate a federally funded needle exchange  under new rules proposed by Congress.

The Drug War Chronicle provides an interesting history of the needle exchange shenannigans. Essentially, Obama did not remove the ban from a budget bill because he thinks policy shouldn’t be made through sub-clauses in budget bills. Democrats on the committee discussing the bill disagreed, and dropped the ban. Then Republicans, not willing to give up the idea that the availability of clean needles would have us all racing to start shooting up smack, decided to protect the innocent by forbidding needle programmes within 1,000 feet of “a public or private day care centre, elementary school, vocational school, secondary school, college, junior college, or university, or any public swimming pool, park, playground, video arcade, or youth centre, or an event sponsored by any such entity”. That’s the red bits on the map of Chicago above.