This is an interesting map to play around with. It allows you to see how many 15-minute neighborhoods and cities there are around the world. And it works by calculating the average time it takes to walk or bike to the closest 20 points of interest in 10,000 cities. These points include all of the usual suspects like places of work, schools, healthcare institutions, grocery stores, and so on. A blue cell indicates an average walk time < 15 minutes, and a red cell indicates an average walk time > 15 minutes. The darker the color, the shorter or longer the average time in minutes.

By this measure, it's hard to beat many/most European cities. Here are Paris and Barcelona:

The city propers are completely blue, and you have to go pretty far out (or up into mountains) to find areas that don't have 15-minute conveniences.

Toronto has a strong core and isn't terrible overall, but expectedly, we aren't as uniform and as deep blue as Paris and Barcelona:

Where things get really interesting, though, is when you look at cities like Dallas and Houston:

It's clear where these cities stand on walkability.

Boy, population densities can be so misleading. The typical approach is to just take the number of people and divide it by a given area. This then gives you something like X number of "people per square kilometer." The problem with this approach is that there are countless factors that can skew your result.

Hong Kong, for instance, is really dense. But as a city, it also has a lot of green space, mountains, and other undeveloped areas. Only about a quarter of Hong Kong's land is developed. So when you divide total people by its administrative boundary area, it is going to appear less dense than it really is.

One alternative approach is to use a method known as population-weighted density. The way this works is that you take the average densities of smaller more granular subareas and then weight them by the population of each subarea. It is a little more complicated to calculate, but the overall intent is to try and capture a density figure that more accurately reflects what the average person experiences on the ground.

And this is exactly the method that Jonathan Nolan decided to use in his new website CityDensity.com. What his site allows you to do is compare population-weighted densities across various cities, and then see how it tapers off as you move outward from their city centers.

Once again, it is hard to beat Paris' supremely dense mid-rise built form:

Well, that is, until you check out Hong Kong:

Charts: CityDensity.com

This is a great tweet and link:

The link is to a figure-ground map of Paris that allows you to filter its buildings by period of construction. Here's what all of the periods and all of the buildings look like:

Once you play around with the map, it will become obvious that the second half of the 19th century and the early 20th century was a prolific building period for Paris (1231 hectares of area). This is what Samuel was getting at in his tweet.

I would love to see a map like this for every city in the world.