Atlas of Hillforts in Britain and Ireland
The following site has an atlas of hill forts in the Uk and in Scotland showing where hillforts might have been before the Romans. Some are post-Roman such as the one near Inchtuthill where they used stones from the Roman fort to build it. But it gives an indication of population centres and why the Romans placed their forts where they did.
Here is the full interactive Atlas of Hillforts in Britain and Ireland.