← All posts · May 10, 2026 · 5 min read

Drive-time vs. radius: why your service-area map is wrong

Pick a candidate address for your next lumber yard, HVAC branch, or service area. Draw a 10-mile radius around it on Google Maps. That's your catchment, right?

No. It's not even close.

The Tampa example

We tested this against the real PermitFocus data. Pick a candidate site in downtown Tampa, FL — say, an industrial parcel near I-275 and Hillsborough Avenue.

• 10-mile radius: 684 new-construction permits in the last 12 months sit inside the circle.
• 15-minute drive time (real road network): 59 new-construction permits.

The radius answer says "this is a high-density location." The drive-time answer says "actually, you can serve very few of those permits from here." If you bought the yard based on the radius, you'd find out 18 months later why your sales reps can't hit their quotas.

Why this happens

A 10-mile radius assumes the world is a flat, road-perfect grid. Reality has:

• Water. Tampa Bay, Galveston Bay, Chesapeake Bay, the Outer Banks — your radius might cut through 6 miles of saltwater your trucks can't drive.
• Bridges and tolls. Even where the water has crossings, the crossings concentrate traffic. A bridge wait + toll can turn 8 minutes of "as-the-crow-flies" into 25 minutes of "as-the-truck-drives."
• Highway access. Two locations 5 miles apart can have radically different reach depending on which one has interstate access versus which one is stuck on surface streets.
• Traffic patterns. Rush-hour drive-time can be 2-3x off-peak. Sales reps making 5-6 calls/day in metro areas live in this number.
• Geography you don't think about. Mountains, parks, military bases, airports — all carve real holes in your radius.

What drive-time actually measures

An isochrone is the shape of "everywhere you can drive in N minutes from a starting point." It's computed against the actual road network, factoring in highway access, real driving speeds (peak, off-peak, or aggregated), and the physical impossibility of driving over water.

You give it a starting point (your candidate site) and a time budget (15 minutes, 30 minutes, 1 hour). It gives you back a polygon shaped like a starfish — usually elongated along the highways, pinched where water cuts through.

For service-area planning, drive-time isochrones answer the question that actually matters: "of the new-construction permits in the surrounding area, which ones can my trucks actually serve from this location?"

When radius is still OK

Drive-time analysis matters most in:

• Metro markets with significant water (FL, gulf coast, NE coastal markets, anywhere with a major river)
• Markets with traffic chokepoints (Tampa, Houston, LA, NYC, Bay Area)
• Operations sensitive to truck-mile economics — concrete plants, large-load LBM deliveries, anything where the haul itself is a cost line

Radius is fine for:

• Quick first-pass screening across many candidate sites
• Markets that are flat, gridded, and water-free (most of the Midwest)
• Direct-mail or geographic marketing decisions where the math doesn't depend on truck routing

The cheap version of this analysis is to use radius to narrow from 50 candidate sites to 5. The expensive (real) version is to use drive-time on the final 5. Skipping the second step is how you end up with a yard that has 684 imaginary permits and 59 real ones.

How to run the drive-time analysis

Three options, in order of cost:

1. OpenRouteService (free up to 500 requests/day) — public API, accurate enough for catchment planning. You give it a lat/lng and time budget, it returns a GeoJSON polygon.
2. Mapbox Isochrone API — paid, faster, more accurate for high-volume use cases.
3. Google Maps Distance Matrix API — paid, integrates with traffic patterns.

Once you have the polygon, you do a point-in-polygon test against your permit data. Every permit inside the polygon is in your catchment. The cost is one polygon API call per candidate site, then one quick database query.

If you don't want to write any of this yourself, PermitFocus's location analyzer runs drive-time isochrones automatically against the 760,000+ permits we track. Drop pins on candidate sites, pick miles or minutes, see the comparison. We default to drive-time because the difference matters.