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Web mapping is the practice of publishing and using maps through web browsers and web services, rather than as static files or desktop-only GIS output. For a researcher it matters in two places: when you build a map that others must be able to open and reuse, and when you choose which map services and coordinate system your analysis depends on. This guide defines the term, compares the two main OGC map-service standards, and works through the one number every web-mapping user should understand: why Web Mercator stops at about 85.05 degrees of latitude.
What is web mapping?
Web mapping means delivering geographic information over the web: a browser requests map content from a server (or from pre-built files), and the map is drawn on the user’s screen, usually with zoom and pan. The result is called a web map. Familiar examples are the base maps of Google Maps and OpenStreetMap, which use the same projected coordinate system (EPSG:3857, discussed below).
The Open Geospatial Consortium (OGC) publishes the standards that let different servers and clients exchange maps. See CASRAI’s guide to the Open Geospatial Consortium for the organisation itself.
Web mapping vs web GIS vs a geoportal
Web mapping focuses on presenting and serving maps. A geoportal is a discovery layer: a catalogue where datasets and map services are described and found. CASRAI’s geoportal guide covers catalogues and spatial data infrastructure; this page covers the map delivery itself. Desktop tools such as QGIS (see how to use QGIS) can both consume and publish these services.
How is a web map served? WMS vs WMTS
Two OGC standards cover most map-image services. Both return images, not vector data, but they differ in how images are produced.
| Item | WMS | WMTS |
|---|---|---|
| Full name | Web Map Service | Web Map Tile Service |
| Version named on the OGC page | 1.3.0 (OGC document 06-042) | 1.0.0 (OGC document 07-057r7); Simple Profile 1.0 (OGC document 13-082r2) |
| What OGC says it is | A simple HTTP interface for requesting geo-registered map images from distributed geospatial databases | A standards-based solution to serve digital maps using predefined image tiles |
| What the server returns | A map image (for example JPEG or PNG) for the area and settings you request | Pre-rendered image tiles that the client assembles into a map |
Sources: OGC WMS standard page and OGC WMTS standard page, both read 2026-11-08 (ogc.org/standards/wms, ogc.org/standards/wmts).
Because WMTS uses predefined tiles, a tile service can answer many users from fixed, reusable images, while a WMS lets the client ask for a custom view. When you cite a map service in a methods section, name the standard, its version and the service endpoint, since the same layer can behave differently over WMS and WMTS.
Why does Web Mercator distort maps? A worked example
Most web base maps use EPSG:3857, called WGS 84 / Pseudo-Mercator or “Web Mercator”. The EPSG registry entry describes it as a projected 2D coordinate system in metres on WGS 84, with an area of use from 85.06 degrees south to 85.06 degrees north, and states that it is not a recognised geodetic system. It is a spherical development of the Mercator projection, so it is not truly conformal. Compared with the ellipsoidal World Mercator (EPSG:3395), the entry reports about 0.7% scale error and northing differences of up to about 43 km on the map (about 21 km on the ground) (epsg.io/3857, read 2026-11-08).
Where the 85.05-degree limit comes from
On a sphere of radius R, the Mercator northing is y = R · ln(tan(π/4 + φ/2)), where φ is latitude in radians. The east-west extent of the world is x = ±πR. A square world map therefore stops where y = πR, that is where ln(tan(π/4 + φ/2)) = π.
- Solve for φ: tan(π/4 + φ/2) = eπ, so φ = 2 · arctan(eπ) − π/2.
- The equivalent form is φ = arctan(sinh(π)). Here sinh(π) ≈ 11.5487.
- arctan(11.5487) ≈ 1.48442 radians ≈ 85.0511 degrees.
This agrees with the 85.06 degrees listed in the registry, which rounds the bound outward. Everything poleward of about 85.05 degrees is not on a standard web base map.
Interpretation: what the limit means for your work
| Situation | Reading guidance |
|---|---|
| Study area between about 85 degrees S and 85 degrees N | Base-map display works; EPSG:3857 is a display convenience. |
| Study area includes polar regions | Beyond about 85.05 degrees the web base map has no coverage; use a projection suited to the polar region. |
| Measuring distance or area | EPSG:3857 is not a recognised geodetic system, and the registry reports about 0.7% scale error against EPSG:3395; reproject your data to a suitable projection before measuring. |
Assumptions and common mistakes
- Treating a web map as a measuring instrument. A display projection is not an analysis projection; reproject first.
- Not stating the coordinate system. Record the EPSG code of any layer you publish or analyse, and describe it in your metadata.
- Citing “Google Maps” instead of the service. Name the data source, service type, version and date accessed.
- Assuming WMS and WMTS are interchangeable. Check which one a provider offers and which your client supports. NASA’s public imagery browser is one example of a service you can inspect; see NASA Worldview.
How to calculate the latitude limit in Excel, R or Python
Excel: =DEGREES(ATAN(SINH(PI()))) returns 85.0511287798066.
R: atan(sinh(pi)) * 180 / pi
Python: import math; math.degrees(math.atan(math.sinh(math.pi)))
FAQ
What is web mapping in simple terms?
It is making, serving and viewing maps through the web, so that a browser can display geographic data without installing GIS software.
What is the difference between WMS and WMTS?
Per OGC, WMS is an HTTP interface for requesting geo-registered map images, while WMTS serves maps using predefined image tiles.
What coordinate system do web maps use?
Most popular base maps use EPSG:3857 (Web Mercator), which covers about 85.06 degrees south to 85.06 degrees north.
Sources
- OGC, Web Map Service (WMS) standard page, ogc.org/standards/wms, read 2026-11-08.
- OGC, Web Map Tile Service (WMTS) standard page, ogc.org/standards/wmts, read 2026-11-08.
- EPSG registry entry as displayed at epsg.io/3857, WGS 84 / Pseudo-Mercator, read 2026-11-08.
