Get positions nearby WP7(Bing map)

I'm working on开发者_StackOverflow a WP7 application that should work this way : After the user had checked- in, he clicks a button which should display the map(Bing-map) with other users who are nearby.

What should the query be so that to find all marks which are +/- 1 (or any other distance) from him?? (Eg if he is at 22.515578,33.265897 then it should search for others which are eg at 21.515578,32.265897 or 23.515578,34.265897)

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Wikipedia is your friend on the topic of how GPS coordinates work.

Without you telling us how you plan to get the data from the other users (local database, or service), your question cannot be answered more explicit.