This is an interesting idea—something we've been thinking about. Tracking at the city level like you're talking about would be fairly straightforward. Tracking individual gas stations within in a city would another level of complexity. To do this right I think we'd need to track gas stations, and so far we haven't been able to find a solid database of stations.
The other piece adding complexity is that you'd need a location-aware smartphone to make this easy. We already optionally track the longitude/latitude for you with
Fuelly Mobile, but getting the correct gas station (or even a list of nearby stations) is another level of complexity. It's possible we could tap into
Foursquare's location API—that's something we've thought about.
But the reality is that most fuel-ups are added here at the website long after the fuel-up has taken place. In that case when you're at a keyboard, it's not so bad to type in the location. So we haven't felt like Fuelly is at the point where this more complicated location-tracking is worthwhile. It might get there someday.
In the meantime, if you fill up via Fuelly Mobile you'll have the longitude/latitude of your fuel-up in a
data export. If you're handy with scripting you could turn those points into a map with fuel price averages. We're not quite ready to take that step here, but it's definitely something to think about.
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