When using rviz on the rosbot_webui demo.launch I can see the LIDAR filling in the map (added in rviz via map topic). Where is that LIDAR map stored? Using rosrun map_server map_saver I can create a map.pgm file. However, I am not sure how the two are related. Ideally I would like to create a map of my environment, do some manual editing of that map, then have rosbot use that edited map.
This map is stored in RAM memory - it is created by gmapping node and it will persist as long as this node is running.
The best way to store the map is to use rosrun map_server map_saver.
The gmapping node is publishing map as nav_msgs/OccupancyGrid message type in topic /map. When you call map_saver it subscribes to /map topic to get single message, saves it to map.pgm and its metadata to map.yaml.
To use created map in the same launch, you need to disable gmapping node: