Namibia is a perfect country to explore Africa as a self-driving traveller. Roads are well maintained, regulations follow international standards and road signs are put at every important point. It is therefore straight forward to find the right way through Namibia.
A map is for 99% of the tourist routes (except for Kaokoveld) the only needed mean of navigation. Different maps exist, but only very few are of good standard. With the free information pack of the Namibia Tourism Board every traveller gets a free map, however, this one is not worth the paper. It only shows major roads and not a lot more. That is why it is called a planning map.
We recommend the following maps for Namibia:
Navigation / GPS
Just like in Europe (where it actually makes sense) a lot of tourists like to travel through Namibia with a GPS / navigation system. Unless you drive to really remote areas in Kaokoveld, a GPS is not needed (it might be a nice gadget though) in Namibia at all. Even in Windhoek it is easy to handle the streets with a map.
For the remote areas there is one good software that is based on experiences of thousands of users. This is called Tracks4Africa and it is available for a few Euro by download. It is only working on Garmin GPS devices. For other GPS there are some standard software that are somewhat good in towns, but not for the serious regions where you would actually need it. You can also just rent a GPS for your time in Namibia, e.g. through Tracks4Africa in Namibia.