transform (crosswalk) data into common location type

[graybeal]

Is your feature request related to a problem? If so please describe.
Data from the same area might only be indexed using different location types. Issue #28 talks about how such data could be found and returned, but the user might need to data organized according to a particular location type.

Describe the solution you'd like
A clear and concise description of what you want to happen.
Data that is organized by location types other than the primary one can be transformed (with suitable statistics if necessary) to fit into the primary location type items that are requested. Mechanisms must be in place to cope with partial overlaps.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.
None, aside from the current model, which is the user does it.

Additional context
Add any other context or screenshots about the feature request here.
This will be especially useful when the original location type is much larger than the location types for the other found data, but can also be appropriate if the measured variables tend to have limited variation within their locations.

Mathew: For PHS they have to crosswalk between different things, e.g., OPTUM changes every year. He has to build his own crosswalk file (PHS crosswalk from zip code to counties is out of date, missed 6000 zip codes).

[Dec 20 2020 interview with PHS researchers]