The grid and map positioning is pretty dumb at the moment (no smart origin computation).
So the starting location for any new map is always the origin of the grid at 0,0 (i.e. when you first create a map or when someone first loads it). However it also remembers where you are (translation, zoom) on the map so you can browser reload at any time and it restores the translation.
Workaround for now (not ideal): when making a new map, don’t pan around before starting drawing… new people loading maps will load at the same origin where the map was created.
Getting lost is definitely an issue I’ve hit before and have thought about either a “reset to origin” button or something a little smarter that notices if you’re way away from any “Active” part of the map then it re centers you on reload.
I really like the infinite grid but I might implement some kind of active boundary with computed center like you suggest.
Technical workaround: You can reset the remembered state by closing all the tabs to the map or deleting the keys in the browsers sessionStorage that start with your map id… you’ll see one called [MAPID].xform that holds the matrix for the current view translation. It’s safe to delete all those keys since they just hold your map session state (selected tool, colors, brush sizes, translations).