Hi Fredy
What are the center coordinates of your regions?
By default, jOpenSim centeres 1000,1000 ... so if your regions are somewhere else, this area most probably just showing ocean
In jOpenSim global settings map tab, you have the possibility to define the default homeX and homeY of the map.
But also in the view (= when you create the menu item for the map) you can set individual map center positions in the tab "Custom map center".
Greetz
FoTo50