Web-based GIS (Web GIS) systems are typically organized in a multi-tier client–server architecture. At a high level, a Web GIS consists of clients (web browsers, desktop or mobile apps) that request geospatial data and services, and servers that provide those services by managing GIS data and performing processing. Commonly this is depicted as a three-tier design: the presentation (client) tier, the application/server tier, and the data tier. The client tier handles user interaction and rendering maps; the server tier (often split into a web server and GIS server) hosts map services and business logic; and the data tier includes databases or file stores holding the spatial data. This model allows clients and servers to communicate over HTTP, often using RESTful APIs.

Figure: Typical Web GIS architecture with clients (browsers or GIS apps), a web/GIS server, and data store. Clients send requests (e.g. map views or feature queries) to the server, which accesses spatial data and returns map images or data for visualization.

This architecture can be implemented on-premises or in the cloud. For example, Esri’s ArcGIS Online is a cloud-based Web GIS where ArcGIS Server and data stores run on AWS/Azure, serving billions of map requests per day. Open-source stacks (e.g. PostGIS + GeoServer + OpenLayers) follow the same tiers. In all cases, clients generate requests (often as HTTP GET/POST calls) and servers reply with geospatial content (images, vector data, etc.). The three-tier layout is flexible – in some deployments a web server (Apache/IIS) sits in front of the GIS server as a proxy, and additional services (e.g. load balancers, caching layers) may be inserted to improve performance.

Client and Server Roles in Web GIS

In a Web GIS, the client and server have distinct responsibilities. The client is typically a user-facing application – for example, a web browser running JavaScript map libraries (Leaflet, OpenLayers, Mapbox), a desktop GIS with a map canvas, or a mobile mapping app. The client’s job is to present the user interface, capture user input (pan/zoom or queries), and render maps using data received from the server. Clients issue requests (for map tiles, feature data, analysis results, etc.) to the server’s APIs and then draw the returned content on the screen. This may involve rendering vector features (points, lines, polygons) on a map or simply displaying bitmap tiles.

The server side typically includes a web server (serving HTML/JS assets) and one or more GIS servers or services. A GIS server (e.g. GeoServer, Esri ArcGIS Server, MapServer) hosts spatial data and provides geoprocessing and mapping services through standardized interfaces. For example, it might expose OGC services (WMS, WFS, WMTS) or proprietary REST endpoints (e.g. ArcGIS REST services). The server handles requests from clients by querying the data tier (databases like PostGIS, file servers, or cloud stores), performing any needed analysis or rendering, and then returning the results. This process often follows the request/response cycle of HTTP: clients send a URL request, the server queries or renders, and then responds. As one explanation notes, “the client can be a web browser or a desktop GIS software and the server-side consists of a Web Server (e.g. Apache Tomcat), Web GIS server (e.g. GeoServer), and a Database (e.g. PostGIS)”.

• Client-side: Sends map/feature requests to the server; displays returned data. Uses web APIs (JavaScript, HTML5) or GIS applications.
• Server-side: Responds to requests by serving geospatial services. Includes:
  • Web server (handles HTTP, security, load balancing).
  • GIS server (implements map/feature services, analysis).
  • Data store (spatial database or file system containing GIS data).

For example, when a user pans a map in the client, the application sends an HTTP request (e.g. for new map tiles or GeoJSON features). The GIS server (e.g. GeoServer) processes the request – querying the PostGIS database or rendering map images – and returns the results to the client. Front-end libraries (Leaflet/OpenLayers) then display the map content.

Data Transmission and Visualization

Communication: Clients and servers exchange data over standard web protocols. A client request (often via AJAX or direct URL access) may include parameters (e.g. bounding box, layer, style). The server responds with data in a web-friendly format. For vector data (features), common formats are GeoJSON or JSON, XML (GML), or KML. For map images, the server returns raster images (PNG, JPEG) or pre-rendered map tiles. For instance, an OGC WMS request returns a map image; an OGC WFS or ArcGIS FeatureService request returns GeoJSON features. These exchanges typically use HTTP GET/POST and URL parameters, making them RESTful by nature.

Once data arrives at the client, visualization occurs:

• Feature/Vector services: The client receives raw geometry and attributes (e.g. GeoJSON) and renders them on the map. The client browser or GIS application draws the points, lines, polygons and applies styling. This gives the client full control over styling and interactivity. For example, a GeoJSON FeatureService returns data that the client’s JavaScript can style dynamically. As noted by one author, “when using feature services, the client is responsible to generate and draw the map based on the data coming from the backend… full control of the geometrical objects”. (The trade-off is that many features can tax the client’s CPU/GPU.)
• Image/Tile services: The client requests map images or tiles (as in a slippy map). The server pre-renders the map (with symbology) and sends back images (PNG/JPEG). The client simply displays these images. This reduces client load at the cost of less interactivity (feature data cannot be individually queried client-side). Popular services include OGC WMS (dynamic images) or WMTS (cached tiles).
• Special services: Clients may also request specific services (e.g. geocoding, routing, or spatial analysis), with servers returning JSON/XML results (such as coordinate pairs or route geometries).

In practice, modern Web GIS clients often use a mix: a basemap may come from a tiled map service (server-rendered), while operational layers (points/lines from a database) come as vector features the client renders. Requests and responses can also be cached at intermediate proxies or CDNs to improve performance. For instance, frequently requested map tiles are cached by CDNs or browsers, reducing server load.

REST APIs: Function and Benefits in Web GIS

REST (Representational State Transfer) is an architectural style for web services that emphasizes statelessness, standard interfaces, and resource-oriented URLs. In Web GIS, RESTful APIs provide a uniform way for clients to request maps, features, or analysis. A RESTful GIS service might use HTTP methods (GET, POST) where each URL identifies a resource (e.g. a map layer, a feature, or a query result) and returns a representation (JSON, XML, image) of that resource.

The functions of REST in GIS include:

• Uniform access: Every GIS resource (map, feature layer, geoprocessing task) is addressed by a URL. For example, an ArcGIS REST endpoint like /rest/services/MyMap/MapServer/0/query can return features from layer 0. This uniform interface simplifies client coding and integration.
• Stateless requests: Each client request contains all information needed (parameters, authentication). The server does not store client session state. This allows easy scaling and load balancing – any request can go to any server instance.
• Standard data formats: REST APIs often return JSON (GeoJSON) or XML, formats easily consumed by web clients. This makes interoperability high, since clients only need standard HTTP and JSON parsers.

The benefits of RESTful GIS services are many. Because REST uses simple HTTP, it is highly scalable and cacheable. As AWS notes, “Systems that implement REST APIs can scale efficiently because REST optimizes client-server interactions. Statelessness removes server load… Well-managed caching… improves response time”. In other words, because each request is independent and can be cached, servers can handle huge traffic (as seen with ArcGIS Online’s billions of map views). REST’s uniform interface and common formats mean that any web framework or language can use the GIS services easily (e.g. a Python script or JavaScript in a browser can call the same REST URLs). Finally, REST APIs fit well with modern web/mobile development and cloud architectures: they can be consumed by AJAX, integrated with frontend frameworks (React, Angular), and deployed on cloud infrastructure with auto-scaling.

In the geospatial world, the move toward REST is exemplified by the OGC’s new OGC API standards. The OGC describes these as “resource-centric APIs that take advantage of modern web development practices,” building on legacy WMS/WFS but using RESTful principles. For example, OGC API – Features is essentially a RESTful successor to WFS, returning GeoJSON via HTTP.

Common RESTful GIS Services

Modern Web GIS platforms offer many RESTful services. Some key examples include:

• Esri ArcGIS REST API: A widely-used suite of services provided by ArcGIS Server and ArcGIS Online. ArcGIS REST endpoints allow clients to retrieve map images, query features, geocode addresses, perform routing, and run spatial analysis. For example, an ArcGIS Feature Service at a URL like https://server/arcgis/rest/services/MyData/FeatureServer/0 returns features in JSON. (Administrators also use ArcGIS REST to manage servers programmatically.) ArcGIS Server itself “supplies mapping and GIS capabilities via ArcGIS Online and client applications”, and exposes them through its REST API.
• OGC Web Services (WMS, WFS, WMTS): The OGC’s classic standards remain common. A WMS (Web Map Service) endpoint accepts parameters (layer, format, bbox) and returns a map image. A WFS (Web Feature Service) returns raw features (in GML or GeoJSON) for a queried area. A WMTS (Web Map Tile Service) provides pre-rendered tiles. These are often implemented in a RESTful manner (simple HTTP URLs). For example, GeoServer (an open-source GIS server) “publishes data from any major spatial data source using open standards,” supporting WMS, WFS, WCS, WMTS, and the newer OGC API – Features. (GeoServer explicitly lists support for WMS and WFS among its OGC services.)
• OGC API – Features/Maps/Tiles: The latest OGC APIs (features, maps, tiles) define RESTful interfaces. For instance, an OGC API – Features endpoint might allow GET requests like /collections/roads/items?bbox=... to retrieve GeoJSON features. These are not always yet as ubiquitous as WMS/WFS but are increasingly supported by platforms (Esri’s ArcGIS, GeoServer, MapServer, and cloud services).
• OpenStreetMap Overpass API: OpenStreetMap (OSM) provides open map data and a RESTful Overpass API for querying it. Overpass acts “as a database over the web”: a client sends an HTTP query and gets back the matching OSM data (in JSON or XML). For example, a map app can request all highways in a bounding box from Overpass via a simple REST query.
• Commercial Map APIs: Major providers like Google Maps Platform, Mapbox, HERE, and Bing Maps offer REST APIs for tile maps, geocoding, routing, etc. (For example, Google’s Geocoding API returns JSON coordinates for a given address.) These are also based on REST principles, though proprietary.

Each service uses standard web methods so clients can easily integrate them. For example, a JavaScript app might fetch a tile at https://server/wmts?layer=basemap&tilematrix=... or call https://maps.googleapis.com/maps/api/geocode/json?address=... – in both cases, using plain HTTP. The uniform style of REST APIs makes building and combining GIS services straightforward.

Example Use Cases and Platforms

Real-world Web GIS platforms illustrate these principles. For example, Esri ArcGIS Online/Enterprise is a full Web GIS platform where ArcGIS Servers publish map and feature services via REST. ArcGIS Online “hosts hundreds of millions of content items and registered users” and “serves billions of maps per day” with high scalability. Its services supported critical use cases like the Johns Hopkins COVID-19 Dashboard: “Built on ArcGIS Online, the Johns Hopkins COVID-19 Dashboard… has received billions of views”under massive load. This shows how a cloud-based GIS (using REST APIs for map/data access) can support global real-time mapping.

Open-source stacks also demonstrate Web GIS architecture. For instance, GeoServer (part of the OSGeo community) is “designed for interoperability” and “publishes data from any major spatial data source using open standards”. Combined with a PostGIS data store and a Leaflet or OpenLayers client, this stack forms a complete Web GIS: clients request WMS/WFS (or OGC API) services from GeoServer, which retrieves data from the database and returns map images or GeoJSON. Many public GIS portals (e.g. government open data viewers) use this pattern.

OpenStreetMap (OSM) itself is a crowd-sourced Web GIS. Its map tile servers and APIs allow both web clients (e.g. the map on openstreetmap.org) and apps to retrieve map tiles and data via RESTful calls. The Overpass API specifically lets developers query OSM data dynamically.

Other examples include Mapbox and Google Maps, which provide REST endpoints for custom map styles and data overlays. In all cases, the underlying architecture is the same: a client-server model where spatial requests and responses flow over the web, and RESTful services provide access to GIS functions.

Key Takeaways: Web GIS architecture is essentially a specialized web application architecture. Clients (browsers or apps) interact with servers via HTTP. Servers deliver geospatial content—either raw data or rendered maps—through standardized RESTful endpoints. This design (often in three tiers) enables scalability, interoperability, and rich interactive mapping in modern applications.