How commute times work

Say you work near the middle of a city and you are willing to travel 30 minutes each way. That single sentence rules out most of the metro area. The problem is that it is very hard to see which part it rules out by looking at a normal map.

That is the job this filter does. You give it a place and a time, and it shades everywhere you could actually live.

Step one: pick where you are travelling to

Usually an office. It can be anything with an address: a school, a hospital, a relative’s house, a trailhead you visit every weekend. The filter does not care what the destination means to you.

Step two: pick how long, and how you travel

Choose a number of minutes, and whether you are driving or taking transit. The map fills in every place that fits.

The shape it draws is rarely a circle. Roads, rivers, bridges and hills all bend it. A motorway can stretch it out for miles in one direction while a river holds it back a few hundred metres away. That shape is the useful part — it is the thing you cannot guess.

Step three: add the rest of your life

A commute on its own is not a home search. The point of drawing it on a map is that you can put other things on top.

Add a rent ceiling. Add the crime layer. Add schools. What survives all of them at once is a much smaller and much more honest list than any of them alone. This is usually the moment people discover which of their requirements is the expensive one.

Two commutes at once

If two people in a household work in different places, run it twice and keep the overlap. Households routinely pick somewhere that is bearable for one person and quietly awful for the other, mostly because the overlap is genuinely hard to picture.

Seeing it drawn tends to settle the argument quickly. Sometimes it shows there is no good answer, which is also worth knowing early.

What the times assume

Worth knowing before you trust a number to the minute.

• Driving times are typical, not worst case. A 30-minute drive can be 50 in the wrong direction at the wrong hour. Treat the boundary as approximate and give yourself margin.
• Transit times come from published timetables. They assume the service runs as scheduled, which is a bigger assumption in some cities than others.
• Walking to and from stops is included, but waiting is modelled from the timetable rather than from how reliable the line actually is.
• It does not know about your life. A nursery drop-off can add twenty minutes that no routing engine will ever see.

Where the data comes from

Road networks and travel-time estimates come from established routing services. Transit comes from the schedules that agencies publish themselves, which is the same data that powers the trip planner on their own websites.

Coverage follows the agencies. Where an agency does not publish a schedule feed, we cannot draw transit times for it, and we would rather show nothing than invent them.

You can draw your own on the commute map, and stack the other filters on top of it.