ESRI Shapefile (SHP)

The shapefile was invented by ESRI in the early 1990s, and it is still the most widespread exchange format in GIS: it is read by ArcGIS, QGIS, MapInfo, GRASS, GeoPandas, PostGIS and by almost anything that can work with a map at all. Formally it is not one file but a set: geometry, an index, an attribute table, a description of the coordinate system and of the encoding.

Data is exported to a shapefile when it goes into somebody else's workflow: hand it to a contractor, load it into a municipal GIS, put it into a project where this has been the practice for years. The format is old and has limitations, but that is exactly why it is guaranteed to open without questions.

What is in the archive: a ZIP where each layer sits in its own folder as a full set of files — roads separately, buildings separately — with a README.txt description next to them. That is not done for looks: one shapefile stores only one geometry type, points, lines and polygons physically cannot live together. The coordinates are WGS84 (EPSG:4326), and the OpenStreetMap attributes are written into the table in UTF-8.

Worth knowing up front: field names are limited to ten characters and long names get truncated, and the geometry file cannot exceed 2 GB. If these limits get in the way — take GeoPackage: the same layers in one modern file and without such restrictions.