Testing location data with edge cases, not just happy paths
An address in a well mapped city center tells you almost nothing about how your system handles a rural route, a disputed border, or a query near the poles. Test the hard cases deliberately.
What ASN data can and can't tell you about a location
Every IP address on the public internet belongs to a block that is, in turn, operated within an autonomous system, identified by an ASN, a number that essentially names which network is responsible for routing traffic for that address range. Looking up the ASN behind an IP tells you which organization operates the network, and that single fact turns out to be a genuinely useful signal, separate from and complementary to the geographic location fields most IP lookups are built around.
What ASN data reliably tells you is the network operator: a specific ISP, a mobile carrier, a cloud hosting provider, a corporate network, or a content delivery network. This is valuable on its own for a range of decisions that have nothing to do with pinpointing a physical location. Distinguishing residential ISP traffic from data center or hosting traffic is a strong, direct fraud signal, since a request claiming to be an individual consumer but originating from a known cloud hosting ASN is inherently more suspicious than the identical request coming from a residential broadband ASN, regardless of what either resolves to geographically.
What ASN data does not reliably tell you is a precise location. A single ASN can span an enormous geographic footprint, a large ISP or a global cloud provider might operate infrastructure across many countries under one ASN, so knowing the ASN alone narrows down the operator, not the place. Even within a single country, one ASN's infrastructure can be spread across many cities. Treating ASN as a location signal on its own, rather than as a complement to the separate geographic fields in a lookup, is a common and avoidable mistake.
The two signals are genuinely most useful combined rather than either one alone. Geographic fields tell you where a request appears to originate. ASN and organization tell you what kind of network it is coming through, residential, mobile, hosting, corporate, which helps you judge how much to trust the geographic estimate in the first place, since, as covered elsewhere, mobile and hosting ranges behave very differently from fixed residential ones for how tightly the IP tracks a physical location.
My Geocode's IPv4 and IPv6 lookups return ASN and organization alongside the geographic fields for exactly this reason, so you get both signals in one response and can combine them according to what your specific use case actually needs, rather than treating either one as a complete answer by itself.