The map below shows concentration of reachable Bitcoin nodes found in countries around the world. The data is sourced using Bitnodes, which is currently being developed to estimate the size of the Bitcoin network by finding all the reachable nodes in the network.
The current methodology involves sending getaddr messages recursively to find all the reachable nodes in the network, starting from a set of seed nodes. Bitnodes uses Bitcoin protocol version 70001 (i.e. >= /Satoshi:0.8.x/), so nodes running an older protocol version will be skipped.
There are currently reachable nodes