The basic question that we seek to answer in this recipe is the fundamental distance question, 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 in two steps. The first step with which we'll approach this is in a simple heuristic way, 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 faster. In the case of a spatial index, it helps us find faster ways, when things...