The technique I used was to drill Google Maps down to the highest magnification, remove modern features and replace them with features and names for the setting. I made extensive use of the Smudge tool to soften the edges of the areas I masked. So far so good,
The hexes are approximately 1 mile center to center, I've added the walls of the town roads and a latifundium centered on the twenty year old remains of the legionary camp (Castra Appius). The black dot on the hilltop is the location of the Castle of the Mad Archmage, just outside of town.
I then selected the center of the image, moved it into a new xcf file and scaled it up by a factor of three. I immediately noticed that the line I had added pixelated badly when they were blown up, but a little editing and running the Smudge tool over them helped with the appearance.
I then started laying out the interior of Scodra, starting with the king's palace and garden at the east end. So far so good. Then the street grid, and because the area is not aligned with the screen pixels, I ended up with jagged edges and blobs. Not great, but reasonable. Then I tried placing the 'Old Fish' by the gate - and even at the scale of this image it's visibly not parallel to the street grid.
Perhaps if I can increase the pixel density in the image or go back and blow up the image further, I can improve the quality. Otherwise I'll leave off buildings and just note the contents of the block.
Not everything succeeds at the first try, the trick is not to be afraid to take the second try.