What is the finest granularity of geo-location that is reliable?

Reading an article this morning I noted a legal case where a service provider was required to discriminate between users from different countries based on IP addresses. I know that 开发者_如何学编程Internet Assigned Numbers Authority (IANA) gives IP addresses in blocks to each of the five Regional Internet Registries (RIRs). And that each RIR covers specific geographical areas. It seems that you can say with high reliability that an IP address in a block given to a RIR is within that RIRs geographical region.

Is it possible to reliably locate an IP address at a finer granularity than RIR region? For example could you reliably say that an IP address is within a country, provence, state, region, county, metropolitan area, city, etc.? Do you think it differs for each of the RIRs?

Baed on an article on Ars Technica 'IP address can now pin down your location to within a half mile' it looks like finer than City resolution. Reliability is based on using known IP-location points and doing triangulation with ping timing. Of course this only works with sufficient known IP-location points, so resolution near high density areas is likely to be better than resolution in lower density areas.