[L41A]

It's all relative. The most important thing is to be consistent with a reference location for each MSA.

For each of 366 MSAs, I chose a reference location and kept it constant. For example, I specified a reference for Atlanta MSA and found its distance to each of the other specified locations of the remaining 365 MSAs. I did this for each of the 13 largest US MSAs. The resulting table could be queried to get an indication of population within any radius of any MSA.

Therefore, changing the reference point for any MSA would change its distance to ALL of the other 365 MSAs. Also while one MSA may drop off within a certain radius, another may be added or vice-versa.