Urban Nature Access: handle the case where an admin boundary doesn't overlap any people

[phargogh]

A user on the forums encountered a ZeroDivisionError that appears to be caused by an admin boundary polygon that doesn't overlap any people in the population raster. The workaround suggested to the user was to locate that polygon and remove it from the vector until a fix can be implemented.

[phargogh]

There is a question about how best to handle this case. As the denominator approaches 0 from the positive side where the available nature area is constant, then the value of the ratio will approach infinity. So what should be the value of the ratio saved in the vector? inf? 0? nan? I've asked Lisa and Roy on slack about this and am waiting to hear back.

[phargogh]

From Lisa:

Let's go with NaN to treat it as undefined, and then state this in the user's guide. Since this is an urban model, I'd expect it's mostly likely to arise either when an admin unit is composed entirely of a park or other area with no residents or the user has input admin boundaries that extend beyond the the population raster. Even though the limit is approaching infinity, making it inf seems more prone to user misinterpretation or to generate misleading results in downstream analyses.