To change the 'active' map layer (i.e. the layer displayed in L3DT's main window), you can use the layer selection tab control at the top of the main window, as highlighted below:
Alternatively, you can use the show map layer window, which is opened by selecting the 'View→Show map layer…' menu option, or clicking on the 'Show map layer' toolbar button, shown below:
These options will open the show map layer window, shown below:
To select a map for display, simply left-click the mouse on it.
Other things to note include:
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