Radius vs. Drive Time vs. Straight-Line Distance: Which Map Should You Use?

A 10-mile radius, a 20-minute drive-time area and a 10-mile road route can all look very different on the same map. They answer different questions. Choosing the wrong measurement is one of the easiest ways to make a map look precise while answering the wrong problem.

Use a radius when distance from one point is the rule

A radius map draws a geographic circle around a center point. Every point on the circle is approximately the same surface distance from the center. Radius maps are useful when the rule itself is distance-based: a delivery policy within 15 miles, a search area around a tower, a school assignment buffer, a rough service territory or a visual comparison between two fixed distances.

• Best for: fixed-distance policies, simple coverage zones and quick geographic comparisons.
• Not the same as: driving distance, walking distance or travel time.
• Main limitation: the circle ignores roads, rivers, mountains, ferries, border crossings and traffic conditions.

Use drive time when accessibility matters

A drive-time map, also called an isochrone, follows the road network and estimates the area reachable within a selected travel time. A 30-minute drive may extend far along a highway but remain small across a river with few bridges. That irregular shape is often exactly what a planner needs.

• Best for: store catchments, commute zones, emergency planning, field-service coverage and meeting-location decisions.
• Interpret the result as an estimate, not a guarantee. Public routing engines generally model roads and typical speeds rather than live minute-by-minute traffic.
• Always state the travel mode and time assumption when sharing the map.

Use straight-line distance for geographic separation

Straight-line or great-circle distance measures the shortest surface path between two locations without following roads. It is often called 'as the crow flies' distance. It is useful for geographic analysis, aviation-style separation, comparing locations consistently, radio-range approximations and any task where the road network is irrelevant.

A worked example

Imagine a customer is 8 miles from a shop in straight-line distance. If a river lies between them and the nearest bridge is several miles away, the road trip could be 14 miles and 25 minutes. A 10-mile radius would include the customer, while a 15-minute drive-time map might exclude them. Neither result is wrong; each describes a different relationship.

A simple decision rule

• If your policy says 'within X miles of this point,' start with a radius.
• If the question is 'who can reach this place in X minutes,' use a drive-time map.
• If you are comparing pure geographic separation, use straight-line distance.
• If money or legal eligibility depends on the result, verify the official rule and data source instead of relying on a generic web map alone.