There are things local people know about, which still diffuse by word of mouth - and I still see paper notices posted on lamp-posts and at supermarket boards. This is why I did an experiment and built lokenote.com
I havent nailed it with lokenote, but it hints theres something there... Im aware this is a first, imperfect approximation of the kind of tool that will enable people to annotate locations. Sometimes you need to build these experiments to see what works or doesn't.
I dont think the storing/retrieving of geo-data is that hard a problem, you can roll your own nested squares approach, or reuse whats there now, eg. Mongo 2d indexes.
Rather, I think the problem is making a nice way to integrate the location dimension into our tools/web apps more seamlessly. eg. a dating chat app might just favour partners close to your location without being told what postcodes to look in. I see this as a 'too many knobs' type problem ( a bit like those search forms you see that have options for 10 different dimensions to filter on, which are better replaced by a single text search field, with hidden smarts. )
So how to bring location to the people, so its useful, effective, un-intrusive and read-write ? I dont think that question has been answered.
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