The National Library of Scotland has the best digital map collection bar none http://maps.nls.uk
Maps can show you neighbouring counties where your ancestors may have met spouses or had children. And they can show you how county boundaries may have changed over time.
The older, John Wood maps (under the tab for town plans and views) show tremendous detail, often including the names of the inhabitants of homes in the town. These tend to be from the very early part of the 1800s.
Old maps are a fantastic resource for giving you a feel for the community that your ancestors lived in. You can see how rural or urban the area was, how large or small the village, what factories, mills, mines, schools, institutions, or other landmarks were in the area. You can see whether the area was mountainous or open field, whether there were any rivers or streams that ran through the area, or whether they were near a lake.
You can overlay maps and see how the area has changed over time - and in many instances can see that very little has changed over time!
You can also plot where your ancestors lived over several decades, using the census returns and valuation rolls. You might be surprised to find that although they may have moved several times, they likely stayed within a 5 or 10 mile radius of where they started.