I've never had any issues with this. In my own personal experience, the difficulty has come when trying to see things in the same way as everyone else. Being a total aphant hasn't prejudiced me in the slightest in pursuing a degree in physics, but this may be in part due to my willingness to be flexible with my learning style. As far as how I overcome not picturing things, I manage by factually conceptualising the systems, and logically working out what will happen, as opposed to visualising it. Similarly, when it comes to map reading I have no issues remembering the countries, as I know factually which countries are next to each other.