Spatial Buffer & Overlay Analyzer
The two GIS operations every site study starts with: buffer (everything within X miles) and overlay (what is in there?). Set a centre and radius and get counts of towns, schools and hospitals inside.
By Aryan Khan, Founder & Editor · Updated October 2026
A 72-point spherical circle and capped OSM node counts provide a preliminary approximation.
How to use Spatial Buffer & Overlay Analyzer
Buffer draws the circle; overlay counts its contents:
Choose a centre and a 1–50 mile radius to draw an approximate circle and count up to 2,000 returned OSM city, town, village, school and hospital nodes. Ways and relations are excluded; results are not complete or official.
- 1Set the centre point.
- 2Choose the radius in miles.
- 3Press “Draw buffer & count”.
What people use Spatial Buffer & Overlay Analyzer for
1. Site selection studies
Candidate sites compared by what their buffers contain — population proxies, facilities, competitors' absence. The Service Coverage Gap Viewer checks the network view afterwards.
2. Planning and impact statements
'Within 2 miles of the proposed site lie 3 schools and a hospital' is a buffer-overlay sentence — this tool produces it with the arithmetic shown.
3. Environmental screening
Protected sites, water features and settlements within a works radius — the screening every assessment opens with.
4. Teaching GIS thinking
Buffer and overlay are the two verbs of spatial analysis. This page lets students perform both before they meet the software that industrialises them.
Worked examples
Doubling the radius from 2 to 4 miles quadruples the buffered ground (12.6 → 50.3 sq mi) — and roughly quadruples everything counted in it. Radius choices are never casual.
A facility just outside the line is outside — overlay counts containment, not closeness. The professional habit is to report a second, wider buffer alongside, so edge sensitivity is visible rather than hidden.
Buffer sizes and their ground
The area each radius commands — the denominator of every count.
| Buffer radius | Area | Typical study |
|---|---|---|
| 1 mi | 3.14 sq mi | Neighbourhood impact |
| 2 mi | 12.57 sq mi | Local screening |
| 3 mi | 28.27 sq mi | Site catchments |
| 5 mi | 78.54 sq mi | District studies |
| 10 mi | 314.16 sq mi | Regional context |
Counts come from open map data (towns, schools, hospitals as recorded) — deep in mapped regions, thinner where mapping is sparse; the page reports the data's answer, not the world's census.
How to interpret the result
The most common errors come from using a correct result to answer the wrong geographic question. Keep these points in mind for Spatial Buffer & Overlay Analyzer:
- Decide geometric vs temporal reach before drawing anything: a 10 km circle and a 15-minute drive area answer different questions, and in car-dependent geography they barely overlap in shape. Circles for policy radii, isochrones for response promises.
- Verify areas against a known object first — measure a football pitch or a city block you know — and you'll calibrate your eye for what a hectare or acre looks like at your zoom. The map preview is the unit your intuition trusts.
Limits & appropriate use
Circles and polygons are geometric truths with semantic limits. A radius says nothing about rivers, one-way systems or response times; an area says nothing about what is inside it. The most expensive misuse is treating a geometric catchment as a service promise — which is why the isochrone tools exist as the temporal counterpart, and why the pages cross-link the two insistently. A second limit is resolution: drawn vertices capture the boundary you click, so curved shores want more clicks, and the perimeter grows (correctly) as you add them — the coastline paradox, politely present in every honest measurement tool.
Within geometry, the numbers are exact on the sphere: areas by spherical excess, boundaries by destination math, exports with their parameters embedded. The escalation ladder is short: cadastral precision needs licensed surveys; population-inside-shapes needs census blocks; drive-time promises need the routing engine. Used as the fast, auditable, shareable geometric layer that feeds those heavier instruments, this is exactly the right tool — and it says so.
- Cadastral/legal area → licensed survey with local datum practice.
- Population inside shapes → census blocks, not city-point sums.
- Response-time promises → isochrones plus operational buffers.
Data & methodology
Geodesic circle polygon via destination points, plus an Overpass around-query tally by feature type.
For source details, licences and model limitations, see Data Sources and Methodology.
Key terms worth knowing
- Spherical excess
- The method for exact polygon areas on a sphere.
- Catchment
- The area or population served from a centre, geometric or temporal.
Editorial guidance: MapBench explains the method and limitations so the tool can be used as a transparent reference, not as a black-box answer. For legal boundaries, safety-critical routing, surveying, engineering, regulated decisions or official statistics, verify the result with the responsible authority or a qualified professional.
Category: Radius & Area. Results are intended for everyday analysis and planning unless a page explicitly states otherwise.
Method, assumptions & limits
- This tool’s method
- Geodesic circle polygon via destination points, plus an Overpass around-query tally by feature type.
- Before relying on the answer
- Check the centre, radius or drawn vertices and the selected units. A geometric footprint does not describe which roads or entrances are accessible.
- What the result cannot establish
- A radius is not a travel-time guarantee. For parcel boundaries or legal land area, use an authoritative survey.
Coverage: Worldwide. Search, basemap and external data requests may use third-party services; browser-based does not mean every operation is offline. Read the source and licence notes, calculation methodology and privacy policy. If a result looks inconsistent, report a correction with the inputs and mode used.
Frequently asked questions
Clear answers about the calculation, accuracy and appropriate use.
What gets counted?
Up to 2,000 returned OSM nodes tagged as city, town, village, school or hospital; ways and relations are excluded and counts may be incomplete.
Is the buffer a true circle?
It uses 72 spherical destination points joined as a polygon. The displayed area is a planar πr² approximation.
Is a radius the same as driving distance?
No. A radius is a geometric circle around a centre point. Driving reach depends on the road network and usually has an irregular shape.
Can I use this for service-area planning?
Yes for first-pass planning. Use a drive-time or road-network tool when accessibility matters more than straight-line coverage.
Are map measurements legal survey measurements?
No. MapBench measurements are planning/reference outputs unless a page explicitly states otherwise. Use a licensed surveyor for legal boundaries.
What data gets counted?
Only returned OSM nodes with the selected tags are counted, with a combined limit of 2,000. Ways, relations and unmapped features are excluded.
Buffer around a point or a shape?
This analyzer buffers a centre point; buffers around lines and polygons are full-GIS operations built on the same principle.
Counts or lists?
The analysis reports counts for the study; the underlying places are the map's own records, explorable on the linked tools.
Overlapping buffers double-count?
Run separately, each buffer counts its own contents — a place between two sites appears in both studies, correctly for site comparison.
Drive-time buffers?
A refinement: equal-time shapes bend with roads. The circular buffer is the screening standard because it is reproducible by anyone, anywhere.
How big a radius is sane?
The radius control is limited to 1–50 miles. The area shown uses the planar πr² approximation.
Can I analyse several centres?
Run each centre and compare tables — systematic comparison is the method; the tool keeps each run clean.
Related tools and resources
Coverage networks: the Service Coverage Gap Viewer; buffers drawn: the Buffer Zone Map; catchments: the Store Catchment Area Calculator.
More free tools
Sources, methodology & editorial trust
- ✓ Browser-first processing where supported
- ✓ External sources are documented
- ✓ No account required for public tools
- ✓ Review data sources
Calculations are documented with their assumptions, limitations and source context rather than presented as unexplained answers.
Reviewed and maintained by Aryan Khan, Founder & Editor of MapBench.
Part of our radius & service area hub
Spatial Buffer & Overlay Analyzer sits in the radius & service area cluster, alongside 18 other tools that answer neighbouring questions with different methods or datasets.
You may also need
When this answer is only part of the job, these clusters cover the next step.
Read the guide behind this tool
How to Draw a Radius on Google Maps — Google Maps has no radius button. Here are the exact workarounds to draw a radius circle — plus free tools that do it in one click.