The radius delivery zone has two failure modes that work against each other. In the directions where access is slow — across rivers, through dense grids, around industrial barriers — the radius accepts addresses that are actually 45 minutes away. In the directions where highways make access fast — the radius excludes addresses that are actually 18 minutes away. Both failures cost money.

The two-sided radius problem for delivery

Consider a food delivery depot on the edge of a city grid, next to a major river. A 3-mile radius extends across the river and includes the residential neighborhoods on the far bank — neighborhoods that require a 12-minute detour to the nearest bridge, then through congested downtown streets, adding 20–25 minutes to each delivery. The depot accepts these orders because they're "within range." The couriers know them as the orders that blow their delivery SLA and generate complaints.

On the other side of the depot, a highway on-ramp provides fast access to a suburban development 4.5 miles away. The radius excludes it. Customers in that development can't order — not because the depot can't serve them, but because the delivery zone was drawn as a circle.

These aren't edge cases. They're the default condition of any radius delivery zone in a city with non-uniform road topology — which is every city. The cost shows up in late deliveries, refunds, and the inexplicable pattern of complaints always coming from the same neighborhoods.

How drive-time delivery zones work

A drive-time delivery zone is an isochrone computed from your depot's location using the actual road network. Set a maximum drive time — say, 20 minutes — and the algorithm traverses every road reachable from the depot within that time, following actual speed limits and turn restrictions. The boundary of the reachable zone is the delivery polygon.

The resulting shape is asymmetric because road access is asymmetric. The polygon extends farther along highway corridors and narrows around bottlenecks. It contracts around the river. It doesn't cross the rail yard. This asymmetry is the point: it tells the truth about where a driver can actually be in 20 minutes.

For delivery operations, this means you accept only the orders you can actually fulfill within SLA. You stop accepting orders from the far bank of the river. You start accepting orders from the highway-accessible suburb. Net result: fewer late deliveries, lower cost-per-delivery, and delivery zone boundaries that customers can trust.

Setting the right drive-time threshold

The drive-time threshold is the core decision in delivery zone design. It should be derived from your delivery SLA minus operational buffer time:

THRESHOLD CALCULATION

Maximum drive time = SLA time − buffer time
Buffer accounts for: depot loading time, customer interaction time, and return-to-depot routing. For a 30-minute SLA with a 10-minute operational buffer, the delivery zone should be drawn at a 20-minute drive-time isochrone from the depot.

Common thresholds by delivery type:

For time-of-day sensitive operations — morning grocery delivery, lunch food delivery — consider generating separate morning and afternoon drive-time polygons. A 20-minute drive-time zone from a depot at 7am (light traffic) is materially larger than the same zone at noon. Accepting orders based on the morning polygon and fulfilling them at noon creates the same SLA problem as using a radius.

Multi-depot coverage planning

When a delivery network has multiple depots, the analysis shifts from single-origin isochrones to coverage topology: how do the depot catchments relate to each other, where do they leave gaps, and where do they overlap inefficiently?

Generate drive-time isochrones from all depots simultaneously. Map the union of coverage polygons to see total served area. Identify coverage gaps — populated areas outside any depot's catchment. Identify heavy overlap zones — areas covered by two or more depots — where delivery requests can be optimally routed to the closest depot.

Coverage gap analysis directly informs depot expansion decisions. If a significant population center falls outside all existing depot catchments and the delivery demand signal is present, a new depot is justified. If coverage gaps are small and overlap zones are large, the network is over-indexed on existing depot locations and expansion would be more efficient at the gap locations.

Service area boundaries for field service and home services

Field service businesses — HVAC, plumbing, electrical, pest control, landscaping — use delivery zone logic in reverse: the technician travels to the customer, not the other way around. Drive-time zone mapping applies identically, but the business questions are different.

For field service, the primary questions are: what service area can one technician cover in a day (drive-time from home base); how many service appointments fit in a territory that large; and where do technician territories overlap or leave gaps?

A 45-minute drive-time polygon from a technician's home base defines the area they can reach in under 45 minutes. For a 6-appointment day with 45 minutes of travel per leg, a well-routed day stays within that polygon. Service area maps built from drive-time zones enable better dispatch routing, realistic capacity planning, and defensible service area definitions for franchise territory agreements in field service franchise systems.

Step-by-step: building a drive-time delivery zone

  1. Identify your depot address. Enter the depot or fulfillment center address into the mapping tool. For multi-depot operations, add all locations.
  2. Set your drive-time threshold. Calculate your threshold from your SLA minus operational buffer. Use the road network routing mode appropriate to your vehicle type — standard drive mode for vans and cars; custom speed profiles for cargo bikes or motorcycles in urban markets.
  3. Generate and review the polygon. Inspect the polygon shape for anomalies — areas the zone extends into that you know are operationally difficult, or areas it excludes that you know are fast to serve. Adjust the threshold if needed.
  4. Check population and address density. Count the addresses and population within the delivery zone. Cross-reference against your actual order volume by zone to validate that the polygon matches your real delivery pattern.
  5. Export and integrate. Export the polygon as GeoJSON for integration into your order management system, website delivery zone checker, or dispatch routing tool. Use the coordinates to set automated in-zone / out-of-zone order validation.

FAQ

What is a delivery zone map?
A delivery zone map shows the geographic area a delivery operation can service from a given depot within a specified travel time. A drive-time delivery zone uses the actual road network to define this boundary — accounting for speed limits, turn restrictions, and road classifications — rather than drawing a simple radius circle.
How do you calculate a delivery zone?
The accurate approach is to use a drive-time isochrone: set a maximum delivery time, run a road network routing algorithm from the depot, and draw the polygon of all reachable points within that time. This accounts for actual road conditions that a radius ignores. The threshold should equal your SLA time minus operational buffer (loading, customer interaction, return routing).
What drive time should I use for a delivery zone?
For on-demand food delivery (30-min SLA), use a 15–20 minute drive-time zone. For same-day grocery or pharmacy (2-hour SLA), use 30–45 minutes. For next-day parcel delivery, use 60–90 minutes per depot. Always subtract operational buffer time (10–15 minutes for most operations) from your SLA to get the drive-time threshold.
How do you optimize delivery coverage with multiple depots?
Generate drive-time isochrones from all depots at your maximum delivery threshold. Map the union of all coverage polygons, identify coverage gaps (populated areas outside any depot's catchment), and identify overlap zones. For overlapping zones, assign requests to the depot with the shortest actual drive time to minimize per-delivery cost. Use gap analysis to inform new depot placement decisions.