Neighborhood-level assumptions

[spencerrecneps]

@beckymasond
This is out of scope for the current slate of BNA changes, but after thinking more about #48 I realized the best solution might be to allow for targeted assumptions to be applied at a neighborhood level.

This could be operationalized by using a standardized shapefile. The idea is that users would draw boundaries within which a certain set of assumptions would apply. For example, I could use neighborhood boundaries from my city and have a different speed limit assumption for each neighborhood. In many cities, the downtown and inner neighborhoods generally have lower speeds while newer areas with wider roads and a more suburban pattern have higher speeds. At present, we apply a single assumption for the entire area.

We could still use city-wide assumptions if no shapefile is provided, but I could imagine this would be an additional input prepared by cities when they provide their other inputs for the online BNA. Those who wish to get the more nuanced treatment would be expected to create boundaries and enter appropriate assumptions for things like speed, number of lanes, parking, etc.