[Warning] New methodology required in case a new city is formed

[Eric-Liu-SANDAG]

Describe the warning

Although unlikely, the way Estimates are currently run means we will have trouble if a new city is formed. For that matter, we would also encounter the same trouble for annexations, but new cities are more visible. Essentially, because Estimates works on frozen geography, we would have to do one of the following:

1. Keep the geography xref frozen for all years with the new city present. This would mean that, for example, if a new city were to be formed in 2025, then all years of data 2020-2024 would contain the city even though it hasn't yet been formed. This is not ideal, but the plus side is that no changes would be necessary to current code
2. Create functionality to modify the geography xref, which would enable a new city to be seamlessly added in the year that it is formed. The issue is that all our geography backend, basically the whole process of creating MGRA series and freezing them, depends on the idea that once created these xrefs are frozen. So we would additionally need to upgrade [demographic_warehouse].[dim].[mgra] in some way to allow changes to the xref between series. Similar work would need to be done by the GIS team on their copies of the MGRA layer. Any downstream code on these geography changes would also need to be updated, such as Data-Surfer. This is also not ideal, as it would be an incredible amount of work to be done, but the plus side is that our output data would be correct relative to geography changes.

In reality, option 1 isn't really viable, as primary data-sources like the CA-DOF Estimates would likely not provide control data for a city for years that the city doesn't exist. But if we were to do option 2, then we would also be signing up for quite a bit of work. Perhaps the best thing to do is just hope that no new cities are formed