There are dozens of file formats that represent geographic information. In this section, we will focus on three file types: shapefiles, GeoJSON, and TopoJSON.
Shapefiles are the most popular vector-based file format. They contain polygons and lines that represent geographic boundaries. The shapefile format was developed by the company Esri as an open standard to work with Geographic Information Systems (GIS). This vector information can also describe other geographic entities (rivers, lakes, and railroads). In addition, the file format has the ability to store data attributes that are useful when working with visualizations (for example, the name of the geographic object, the type, and some relationships). Most importantly for us, there is a large repository of free shapefiles located at http://diva-gis.org. This repository contains a tremendous wealth of data at different levels of specificity and granularity.