Drive Time Map vs Radius Circle: Which One Should You Use?

People often draw a circle around a shop and call it a ‘service area.’ On a flat map that looks tidy. On the ground it is frequently wrong. A river with one bridge, a highway with no exit, or a mountain road can make a ten-mile radius include places that take forty minutes and exclude places that take twelve. The question is rarely ‘what is ten miles away?’ It is ‘what can I reach in twenty minutes?’ Those are different geometries.

What a radius circle actually measures

A map radius tool draws a geodesic circle: every point on the edge is the same ground distance from the centre, measured on the Earth’s surface, not on the road network. That is the right tool for radio coverage sketches, straight-line exclusion zones, ‘within 5 miles as the crow flies,’ and any rule that is literally written in distance, not time.

• Strength: simple, comparable, independent of traffic data
• Weakness: ignores one-way streets, water, and speed limits
• Good for: buffer zones, crow-flies policies, quick visual scale

What a drive-time (isochrone) map measures

A drive-time map asks a routing engine how far you can go along the road network in a fixed number of minutes. The result is a polygon that bulges along freeways and pinches at bottlenecks. Bike and walk modes produce different shapes again. Free tools usually use free-flow or typical speeds, not live congestion — so peak-hour reality can still shrink the area. Even so, the shape is far closer to ‘who can get here for lunch’ than a perfect circle.

A practical way to choose

• Delivery promise in minutes → drive-time / isochrone
• Regulatory buffer in kilometres or miles → radius
• Comparing two candidate sites → run both and look at the difference
• Walking from a station → walking-time or walk isochrone, not a car radius

On MapBench, try the same centre point on the map radius tool and the drive-time map. The mismatch is the lesson: equal distance is not equal access. For multi-stop days, a route planner answers yet another question — order and total length — which neither a single circle nor a single isochrone fully replaces.

The clean circle is attractive because it hides complexity

A radius is easy to explain and easy to print. That is exactly why it gets overused. The circle treats every direction equally even when the real network does not. A bridge, motorway entrance, toll road, ferry or one-way system can make accessibility strongly directional. If the decision is about travel, the irregular isochrone is often the more honest shape.

Run the same centre through Map Radius and Drive Time Map. Seeing the two shapes together is one of the fastest ways to explain why equal distance and equal access are not the same.

Delivery areas: policy language decides the right map

If a business promises delivery within 10 miles, a radius matches the written rule, though a road-distance policy may still be more operationally sensible. If the promise is delivery within 30 minutes, a drive-time model is closer to the question. Mixing a time promise with a distance circle creates hidden service failures around barriers and slow roads.

Store catchments need people, not just polygons

A larger drive-time polygon is not automatically a better store location. One site may reach empty land; another may reach dense neighborhoods. After mapping access, add population, customer locations or demand data. The isochrone is the geographic filter; the business decision needs another layer.

For rough demographic context, compare the result with Population Within Radius while remembering that a radius population estimate is not the same as population inside a road-time polygon.

Walking and cycling make the contrast even stronger

A pedestrian can use footpaths, crossings and bridges that cars cannot. A cyclist may avoid motorways but benefit from dedicated trails. The right network and travel mode therefore matter as much as the contour time. A car-based isochrone should never be reused as though it represented walking access.

Traffic is the missing layer in many free tools

Many public routing services estimate travel from road type and expected speeds rather than live congestion. A 20-minute polygon generated at noon may overstate access during rush hour. For planning, that can still be useful if the assumption is stated. For a contractual delivery promise, you may need historical or live traffic data and operational testing.

A practical decision framework

For the broader comparison, read Radius vs. Drive Time vs. Straight-Line Distance, which separates all three measurements before they get mixed into one service-area decision.