In this chapter, we talked about projections. We covered what they are and the various different types of projections. Longitude, latitude, and other geographic concepts were also discussed. While we just scratched the surface of these pretty complex topics, you should have enough fundamental information to understand how to use projections.

We also talked about the ol.proj.Projection class and the namespace ol.proj associated for coordinates' manipulation, along with how to transform coordinates and use the Proj4js library. You'll often work with data in coordinate systems other than EPSG:4326, and knowing how to work with and transform data in other projections is important. Because Proj4js alone is not useful without OpenLayers 3, we also reviewed the different use cases for managing projections in a layer context, depending on the main layer type, for example, vector or raster. It can be useful to know reprojection in vector when you want to manage projections in the various ol.format classes we already discovered in Chapter 5, Using Vector Layers.

Now, after reviewing how projections work, it's time to review how interactions components work. Without even being aware, we already use them but never really highlighted them until now. When you pan the map for instance, you are already using interactions. Let's dive into the next chapter, Interacting With Your Map.