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Per km²: density, explained simply

A count of 14 means little on its own. 133 per km² is a number you can compare with any city on earth. Here is what 'Per km²' does, when to prefer it over 'Per 1 000 residents', and what it shows for bars across London.

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ByTinkal Gogoi(LinkedIn profile, opens in a new tab)September 4, 20266 min read

Fourteen of what, exactly?

An area on the map has 14 bars. Is that a lot? Compared with the next area, maybe. But you cannot compare it with a street in Manchester, a planning report, or your own sense of what “busy” means, because 14 has no unit of space attached to it.

Per km² attaches one. Every MapBees area is about 0.105 km², so 14 bars becomes 133 bars per km² - a density, and a number that means the same thing in any city on earth. It is the simplest formula in the series, and the one whose value is easiest to underrate.

Per km²the field's term: Density

Bars per km² within a 10-minute walk. Density is peaky by nature: Soho and the City light up, and almost everywhere else is a fraction of them.

If every area is the same size, why bother?

Three reasons, and the third is the one people miss.

A unit anyone can compare

133 per km² can be set beside a figure from another city, a report, or a rule of thumb. 14 cannot, because nobody else uses our area size.

Walks and drawn areas are not all the same size

Within a 10-minute walk an area's neighbourhood can be smaller at the edge of the data; a drawn area can be any size. Per km² keeps those honest.

It is the other kind of ratio

Per 1 000 residents asks how well people are served. Per km² asks how packed the ground is. Nightlife, footfall and competition are ground questions.

Switching it on

Where to click

  1. Map type
  2. Amount
  3. Bar
  4. Count as: Per km²
  5. Look at: Within a 10-minute walk
'Per km² · Density' in the badge. We read it within a walk so that the map shows districts rather than single blocks.
The same 'Count as' row every count carries. Per km² is available for any count, because land area is never missing.

Reading the map

Density maps are lopsided, and that is true, not a fault. A handful of streets in central London have hundreds of bars per km²; most residential areas have a few. The legend spans the whole range, so the centre glows and the suburbs sit dark.

The ramp runs from zero to London's densest neighbourhood. A single extreme district stretches it - the same effect the 'Lowest to highest' scaling post describes.
Hovering an inner-London neighbourhood: 99 bars per km² within a walk. Central Soho is roughly ten times that.

The maths, honestly

Bars per km² in one area
Bars counted
14
Area's sizeone MapBees area, about 350 m across
0.105 km²
Per km²
14 ÷ 0.105 = 133 per km²

Within a walk, both the bars and the land are totalled over the area and its neighbours before dividing, so the density stays a density.

Click any area and the inspector writes the division out with that area's real count and real size.
No small-numbers note here, and that is correct: land area is never tiny the way a resident count can be, so a density is shown exactly as computed.

Density is never 'adjusted for small numbers'

The per 1 000 residents post explains why a rate with three residents underneath it has to be pulled toward the city's value. A density has no such problem: 0.105 km² is 0.105 km² whether ten people live there or none. What density does inherit is the count's own coverage - an area with no data has no density either.

Open bars per km² in London

The whole idea, in four lines

  • Per km² = count ÷ the area's size in square kilometres. 14 bars in a 0.105 km² area is 133 per km².
  • It turns a count into a unit you can compare with any city, report or rule of thumb.
  • It keeps walks and drawn areas honest, because those are not all the same size.
  • Density maps are peaky by nature: the centre glows, the suburbs sit dark, and the legend tells you the range.
  • Use per km² for ground questions - footfall, nightlife, competition - and per 1 000 residents for people questions.

Quick questions

What does 'Per km²' calculate?

The count in an area divided by the area's size in square kilometres. A MapBees area is about 0.105 km², so 14 bars in one area is about 133 bars per km².

If every area is the same size, why bother?

Because 133 per km² is a unit anyone can compare with another city, a report or a planning document. 14 is not. It also keeps a drawn area or a walk honest, since those are not all the same size.

When should I use 'Per km²' instead of 'Per 1 000 residents'?

Use per km² when you care about how packed a place is on the ground - nightlife, footfall, competition on a street. Use per 1 000 residents when you care about how well the people living there are served.

Does density get adjusted for small numbers?

No. The base is land area, which is never tiny in the way a resident count can be, so a density is shown exactly as computed.

See it on a real map

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About the author

Tinkal Gogoi(LinkedIn profile, opens in a new tab)Founder & Location Data Engineer

Builds MapBees's location-intelligence pipeline end to end — census and Overture Maps ingestion, H3 hex scoring, and the map interface — and writes the methodology behind every number on the site.