Apart from the fact that "geographically close" does not always coincide with "network-wise close", that's essentially the principle behind route aggregation as

Apart from the fact that "geographically close" does not always coincide with "network-wise close", that's essentially the principle behind route aggregation as used by routers today. However, applying it successfully to IPv4 is severy compromised because, due to rampant address space fragmentation during the last years, increasingly longer prefixes (i.e., smaller address blocks) have had to be assigned. IPv6's much larger address space makes it unlikely that the routing table will ever become that fragmented in the foreseeable future.