Show sidewalk data at one more zoom level out #179
Description
This may be useful for parcel data, too. But for sidewalks, some of the lines are long. If the user zooms out to see the whole sidewalk, the data might disappear.
If we run into trouble with parcels or buildings at that zoom level, then we can try having a rendering cutoff based on number of points rather than number of objects. Right now we have a zoom level rendering cutoff and a separate object-count cutoff, to make sure we don't get ourselves in trouble.