The basic question that we seek to answer in this recipe is the fundamental distance question, "Which are the closest (name what you are searching for) to me?", for example, "Which are the five coffee shops closest to me?" It turns out that while it is a fundamental question, it's not always easy to answer, though we will make this possible in this recipe. We will approach this with two approaches. The first way in which we'll approach this is in a simple heuristic, which will allow us to come to a solution quickly. Then, we'll take advantage of the deeper PostGIS functionality to make the solution faster and more general with a K-Nearest Neighbor (KNN) approach.

A concept that we need to understand from the outset is that of a spatial index. A spatial index, like other database indexes, functions like a book index. It is a special construct to make looking for things inside our table easier, much in the way a book index helps us find content in a book...