In PS go to the layers palette. Make the background layer black. Add a new layer to draw the map on.
Now select the line tool. U can choose in the menu to either draw so called paths, shapes or pixels. To start with just select pixels. Make sure the new layer is selected when you draw. The color you use is not important now.
Now draw your map. Right click on the new layer and select layer styles. Here you can select another color, 3d effects etc..
HF