At the moment - this is just a conceptual map but after a nuclear war in will be important to identify hazards nation-wide (indeed world-wide). Radioactive dust can blow anywhere - and disintegrating non-maintained nuclear plants could be a major source.
There could be seas of residual radiation from such plants. The radiation from nuclear weapons will pretty much disintegrate and dissipate within a couple of weeks after the last weapon is used - but non-functional nuclear generating plants and their storage of nuclear waste could be another problem. It is a problem that will have to be dealt with.
In the meantime - it will be necessary to track the problems. There may be areas that one cannot drive through - sort of seas or lakes of radiation. They just have to be identified. We don't drive through other lakes and seas now. But this shows one importance of these maps.