Use server-client distance restriction or tuning

[critzo]

Geographic aggregate analyses might use some sort of server-client distance to filter tests to far away servers. Items to consider:

• what is an acceptable distance between server and client?
• is geographic distance the right/only consideration?
• because analysis of traffic to nearest and further away servers are both interesting for different reasons, should our methods include both, to look at different aspects of connectivity (near/far)