We use multilateration to independently determine the location of a server. Multiple servers will ping the IP address and record the round-trip time. There is a limit on the distance light can travel through optical fibre cables in this time, which constrains the possible distance from the server performing the ping. Combining the constraints from multiple servers provides an area that the IP address is truly located within.
RIPE Atlas is one of the sources used to calculate our geolocation data. RIPE Atlas is a dynamic, global network of thousands of probes that have been measuring Internet connectivity and reachability in near real time since 2010. Anyone can directly access the data collected by RIPE Atlas, as well as Internet maps, graphs, tools and analyses based on the aggregated results, at https://atlas.ripe.net. RIPE Atlas was developed and is operated by the RIPE NCC, along with the help of thousands of volunteers. The RIPE NCC is one of five Regional Internet Registries (RIRs) that support the global operation of the Internet.