New feature: Map of Places in a given year

If you visit the map of Places, you'll see new text below the map, that looks something like this:

It's a new feature I'm trying out, that I hope can make the map more useful when trying to put a date on old photos.

The currrent map has become a victim of its own success. If you look at Central using the 1901 map overlay, there are so many markers it is difficult to see what's there: https://gwulo.com/map-of-places#17~22.28175~114.15710~Map_by_GovHK-Markers-1901_HK~100

Here's the new map, only showing Places that existed in 1901: https://gwulo.com/map-of-places-in-year?year=1901#17~22.28175~114.15710~Map_by_GovHK-Markers-1901_HK~100

It's put forward for your feedback on if it's a useful feature that is worth developing, and for any ideas on how the user interface should work to make it easier to use.

Regular readers will note that the second map is missing a lot of markers for buildings that have a Place page on Gwulo, and that definitely existed in 1901. The problem is that the map can only show Places that have values entered for Current condition and Date completed (and also for Date closed / demolished if the Place is already demolished.) 

Here are lists of Places that are missing one or more of those pieces of information. If you can edit and update a Place on the list, the Place will be removed from the list, and appear on the map:

• Places missing ‘Current condition’
   
• Places missing ‘Date completed’
   
• Places missing ‘Date closed / demolished’