When you save your Geographical Map opCharts will store the center location of the map and zoom state. However, when used in a Dashboard, the final display size will be driven by the size of the Component window the Map is contained within. Some testing and adjustment may be necessary.
As of opCharts version 3.2.2 you can Zoom Lock the maps preventing them from zooming in and out when you scroll your mouse wheel. This option can be toggled on or off by the check box as shown in the screenshot below: