Geoportal Bayern is the access point to the spatial data infrastructure of Bavaria (GDI-BY), run by the Bavarian Surveying Administration. It lets you search and visualise geodata from state, municipal, and private providers, and powers the BayernAtlas map viewer.
The Bavarian Surveying Administration provides a growing set of free open geodata — topographic maps, aerial imagery, elevation, and more — via downloads and WMS/WMTS/WFS services through its OpenData portal. It is the authoritative regional source for Bavarian base mapping.