3. Cleaning Procedure

As both Murdock and GREG geo-databases were manually recovered from historical maps, many measurement errors might exist due to the geo-referencing process. For instance: (i) polygons borders could be miss-located due to manual process, (ii) There must be complex geometries that cannot be intersect with other polygons, among others. These errors could increase when intersecting both geo-database.

In order to minimize the number of intersection we employed the following strategies:

• Geometries Checkers: We filtered out those intersection whose geometries were invalid.
• Buffer around the borders: In order to delete the potential geo-referencing mistakes, we create a 5km buffer around the Murdock’s borders. Then, we deleted those intersection that were completely contained in this buffer. In this way, we are sure that we are not including intersections that are likely due to the geo-referencing process.