networking - Estimating distance between two servers by IP address - Server Fault
That's called an IP numbering plan and would be similar to how POTS telephone numbers have a country code prefix, an area code and a local subscriber number and are not completely randomly assigned.
You can then infer similar information, the same area code is in the same DC, an area code +1 or -2 is still nearby or possibly a different quadrant in the same DC and a large off-set in area codes or a different country code is almost certainly long distance.
Which is much more than "everything within the same subnet must be nearby" that would be the only safe assumption to make otherwise, without consulting routing tables.
For instance when ip-address ranges are assigned on a as needed policy, you could get that 10.1.2.0/24 ends in up Ireland, 10.1.3.0/24 in Hong Kong, 10.1.4.0/24 ends in up Los Angeles, with 10.1.5.0/24 in San Francisco nearby and 10.1.6.0/24 bringing you all the way to Sydney.
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