The difference in one line
A radius map draws a circle. Every point within X miles of your workplace, ignoring roads entirely.
A commute time map draws the shape your commute actually makes. Every point you can reach within X minutes, following real roads at real speeds. Sometimes called an isochrone map.
The circle is symmetrical. Your commute never is.
Why the circle misleads
A 20-mile radius around your office includes places you can reach in twenty minutes and places you cannot reach in an hour.
Three things break the circle:
Water. A bay, river or harbour means the nearest crossing may be miles out of your way. Somewhere five miles away in a straight line can be a twenty-mile drive.
Freeway geometry. Areas along a freeway are reachable far faster than areas the same distance away with no highway access. A time map stretches out along the corridors — often dramatically.
Direction of travel. Employment concentrates at one end of most corridors, so traffic loads inbound in the morning and outbound in the evening. A location on the light side of that flow is effectively much closer than an identical distance on the heavy side.
That last one is invisible on a radius map and it is frequently the single biggest factor.
What a commute time map actually shows
The result is rarely a circle. Typical shapes:
- A star or starfish — stretching along freeway and rail corridors, pinching between them
- A half-moon — where water or mountains block one side entirely
- A lopsided blob — where the dominant traffic direction makes one side far cheaper than the other
That shape is the real answer to “where could I live and still get to work in 30 minutes.”
The setting most people get wrong
Set the time of day to the hour you would actually travel, in the direction you would actually travel.
A commute time map generated for free-flow conditions can show an area two or three times larger than the one reachable at peak. If you are house-hunting on the basis of a map built at 11 a.m., you are looking at a fantasy.
Generate two: one for your morning departure, one for your evening return. They will differ, and the smaller one is the one that governs your life.
When a radius map is still fine
Rough filtering. If you need to eliminate obviously-too-far areas quickly, a circle does the job.
Contractual or policy definitions. Where an employer or agency defines a commuting area by mileage — the roughly 50-mile local commuting area used in US federal employment, for instance — the circle is the definition, whatever the roads do.
Estate agent search filters. Most property sites only offer radius search, so you use what exists and then check the real travel time on the shortlist.
Using these for a property search
A workflow that avoids wasted viewings:
1. Draw the radius map first to eliminate the obviously impossible.
2. Generate a commute time map for your actual departure hour and direction. Note which parts of the circle drop out.
3. Look at what the shape follows. The arms stretching outward are freeway and rail corridors — those are where you get the most house for the least commute.
4. Drive the shortlist at your real commute hour. Not at the weekend, not at midday. Tuesday at 8 a.m.
5. Check the return trip too. They are frequently different, and the evening one is often worse.
The variability question a map cannot answer
A commute time map gives you one number for a location. What it cannot show is the range.
A 35-minute commute that ranges from 30 to 40 minutes is a very different life from a 35-minute commute that ranges from 25 to 70. The second one forces you to plan for 70 every day.
Before committing to a location, the number worth knowing is the spread, and the only way to get it is to measure across a week.
Before you decide
A map is a snapshot. A commute is a range.
BoardSpy tracks a real route across real days and shows you the spread rather than the average — so you know what a location will actually cost you before you sign anything.
Frequently asked questions
What is a commute time map?
A commute time map, sometimes called an isochrone map, shows every location you can reach from a starting point within a given travel time. Unlike a radius map it follows real roads, so the shape stretches along fast corridors and pinches at bottlenecks.
What is the difference between a commute radius map and a commute time map?
A radius map draws a circle of fixed distance around a point, ignoring roads. A commute time map shows what is reachable within a time limit along actual roads. The time map is far more useful for a real commute, because travel time is not proportional to straight-line distance.
What time of day should I set when using a commute time map?
Set it to the hour you would actually travel, in the direction you would travel. A map generated for free-flow conditions can show an area two or three times larger than the one reachable at peak, which is misleading if you are choosing where to live.