Design a PROXIMITY SERVER's backend - especially how do you want to store geo-location data, and algorithm to answer the query.

Given: N places. Place p has location (x_p, y_p). Other attributes ..
Query q which consists of (a) query location (x_q, y_q), (b) query distance d_q
Response: {p | distance(p, q) = distance((x_p, y_p), (x_q, y_q)) <= d_q }

Return ALL places within a given query distance from a query location.

Examples.
1/ User walking in downtown Albuqurqe. “Get all restaurants within ½ mile”. Here d_q = ½ mile, (x_q, y_q) is query location. For simplicity, we will use places instead of restaurants

2/ User planning a trip to Oslo while she is still in San Francisco. “Get all places of interest within 200 miles of my hotel in Oslo”. Here d_q is 200 miles, and (x_q, y_q) is the hotel location in Oslo. Again for simplicity, we will use
places instead of places of interests