This hackathon had many people with an interest in maps come together in Zurich. There were several challenges they faced; how to represent maps in a wiki, how to store them and what do we need to know about them in Wikidata. In this mix of challenges the differences between contemporary maps and historic maps feature as well.
Wikidata needs to know several specific things; it needs to know that something is a map, it needs to know the four corners of a map, the location where that map can be found and finally it is nice to know what type of map it is. More attributes are possible but this was considered the minimum for Wikidata.
The thought process about Commons was forward looking; it is going to be "Wikidatafied" and this will surely affect current practices. Information that is currently in templates will move into Wikidata and many of the galeries and categories will surely become redundant because queries will provide a more reliable and complete result.
For Wikis, current best practices were analysed and, it was found that information on a map exists in many layers. There is a base layer and on top of that you can show a contemporary or historic map. On top of it you may want to show the shapes of countries or districts. These may be sprinkled with pointers that reflect the result of a query. To finish it off, you may want to add even more that demonstrates a point made in a particular article.
All this information needs a place. It needs a special place because you may want to use a map several times. In Zurich we ended of a working example of a map that included all these complications by inserting information in a namespace. The next challenges are to make it robust and user friendly enough.