Catchment bands, Reach and Rush hour: catchments from one pin

How many people live within a 5, 10 and 15-minute walk of Trafalgar Square?

About 11,372 residents live within a 15-minute walk of Trafalgar Square: about 827 within 5 minutes, 3,453 more between 5 and 10 minutes, and 7,092 more between 10 and 15. MapBees draws all three walks from one pin in a single step, as Catchment bands, and counts every hex - one hexagon, about 350 m across - in the smallest band it falls in.

Catchment bands live in the Territory tool, beside two companions this post also covers: Reach, which adds up the places in the bands with nearer bands counting more, and the Rush hour tab, which draws one drive at different times of a typical week to show how much it shrinks.

Catchment bands

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The idea, in one sentence

Draw several catchments from one pin at once, nested inside each other, and count each hex once - in the nearest band that reaches it. A catchment (an isochrone) is everywhere you can get to from the pin within a set time, along streets and paths. Nesting them turns one number into a profile: how much is right by the pin, and how much only comes with a longer trip.

Where to click

Open the Territory tool. At the top of its panel sits the pin shelf - Pins, Shared by every section - with a Drop pin button: press it and tap the map. A pin is only a place; each tab picks its own travel mode and minutes from it, so you drop a pin once and use it everywhere.

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There are four sets of bands: 5 · 10 · 15 min, 10 · 20 · 30 min, 15 · 30 · 45 min and 3 · 6 · 9 · 12 min. A travel mode only offers the sets whose outer band fits its own time limit. Each draw is kept in a Band sets list, with an eye to show or hide it on the map, so you can draw from several pins and switch between them.

Reading the bands

The open band set shows one card per measure, with one bar per band. Before you pick anything, the card is the city's residents. Above the cards, the pills under The band the map uses as the area choose what the map draws: pick a band and the map - and the Score - use every hex up to its outer edge. Pick 5–10 min and the area is the whole 10-minute catchment.

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The headline on each card is the whole catchment (11,372 within 15 min); the bars are the bands on their own. Here the outer band holds more than the two inner ones together: most of the residents within 15 minutes live a real walk away, not next door.

+ Add measure opens Measures for your catchments - one list for catchment bands and rush-hour checks; your Score keeps its own. Up to four measures show at once. A count, such as residents or cafés, gets a bar per band; an average, such as a share of residents, gets a dot per band on one strip, because averages never add up across bands.

Reach: the places in the bands, nearer counting more

Add a measure that counts places - cafés, say - and its card gains one more line under the bars, in the form “Reach: about 32 cafés' worth, nearer counting more”. That is Reach: the places in each band, added up with a weight that falls the farther out the band lies. A café 3 minutes away counts more than one 13 minutes away.

Reachthe field's term: Hansen accessibility

Each band's weight is set by its middle minute: exp(−middle minute ÷ 8). For 5 · 10 · 15 minutes the middles are 2.5, 7.5 and 12.5, so the weights are 0.73, 0.39 and 0.21. Other bands get their own weights the same way - for 10 · 20 · 30 minutes, 0.54, 0.15 and 0.04. Hover the Reach line and it lists each band's count and weight.

Reach is a number for comparing, not a count of anything. It is most useful between two pins drawn with the same bands and travel mode: the one with the higher Reach has more of the places close by, not just more of them somewhere in the catchment.

To use one band on its own, press Add the 15-minute catchment to Areas - the button follows the band you picked. It copies that catchment into the Areas tab as an ordinary area, with its own full dashboard, and the band set keeps all its bands.

Rush hour: how much a drive shrinks at a busy time

The third tab asks a driver's question: how far does a 10-minute drive from here really get at 8 in the morning, compared with the afternoon? It draws the same drive catchment at two to four times of a typical week and compares how many residents each reaches. The time that reaches the most is the baseline; the share of residents another time loses against it is the Rush-hour shrink.

Rush-hour shrink

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Nothing runs until you press Check rush hour. Each check is kept as a rush-hour area in a list - Pin 1 · 10 min drive - with an eye to show or hide it. On the map, each time is an outline in its own color, and the time picked under The time the map uses as the area also carries its hexes - the baseline to start with.

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In this capture the result runs against intuition: the 08:00 drive reaches more residents than the 14:00 one. So 08:00 is the baseline, and 14:00 reaches 27,272 fewer - about 24% fewer. That is exactly why MapBees never assumes which hour is the slow one: the baseline is whichever time reaches the most, and the others are compared with it.

Areas, the first tab - catchments you calculate, shapes you draw and areas from your own file - is covered step by step in How to use Territory Mapping.

Open the Territory tool

The whole idea, in six lines

• Drop a pin once; Areas, Bands and Rush hour all build from it.
• Catchment bands draw several catchments from one pin, and each hex counts in the smallest band it falls in.
• The band the map uses as the area sets what the map and the Score read: every hex up to that band's edge.
• Reach adds up the places in the bands, nearer bands counting more: weights 0.73, 0.39 and 0.21 for 5, 10 and 15 minutes.
• Rush hour draws one drive at 2 to 4 times of a typical week; the time reaching the most residents is the baseline.
• Rush-hour shrink is the share of residents another time loses against it - typical traffic, not today's.