Welcome! Congratulations on passing our preliminary quiz. It seems you know enough SQL to start digging into PostGIS. In this part, we'll explain the very basics - what spatial databases are, what PostGIS is, and so on. So, without further ado, let's get started!

First off, we'll discuss what exactly spatial databases are. In the broadest sense, these are databases that have been optimized to store and query geometric data. Most spatial databases provide at least some simple geometric objects: points, linestrings and polygons. Some of them also feature 3D and 4D objects, topological coverages and triangulated irregular networks. Those more advanced features are outside the scope of this course - we'll focus on the basic things that are available in virtually every spatial database.So far, you've probably worked with columns that store numbers (int, decimal, ...), dates, times, strings (varchar, char, ...). You may have also used some functions that deal with these column types, like AVG() for calculating the average of a numerical column. In this course, you'll get to know a new column type that will store points, lines and polygons. Then, you'll also learn about the various functions that calculate the distance between two points or the area of a polygon.

Sometimes you will also hear the names geodatabase, geospatial database or geographical database in place of spatial database. These names highlight the fact that this kind of database can apply geometries to a map to calculate the area of a park, the length of a road, and so on. However, the differences between these names are not that important to us.