GIS Web GIS and Services 5 — Questions and Answers
Question 1: What is the difference between WMS and WMTS in terms of how they serve map images?
- WMS serves vector data; WMTS serves raster data
- WMS renders maps dynamically per request; WMTS serves pre-generated cached tiles (Correct answer)
- WMS supports time dimensions; WMTS does not
- WMS uses REST; WMTS uses SOAP
Correct answer: WMS renders maps dynamically per request; WMTS serves pre-generated cached tiles
WMS generates a custom map image for each request, while WMTS serves pre-cached tiles from a fixed tile matrix, providing much better scalability for high-traffic scenarios.
Question 2: In a Web GIS application, what does 'spatial filtering' in a WFS request allow you to do?
- Change the visual style of returned features
- Request only features that meet a geographic criterion (e.g., within a polygon) (Correct answer)
- Convert feature coordinates to a different CRS
- Limit the number of attribute fields returned
Correct answer: Request only features that meet a geographic criterion (e.g., within a polygon)
Spatial filters in WFS (e.g., BBOX, Within, Intersects) restrict returned features to those satisfying a geographic predicate, reducing data transfer.
Question 3: Which format does the OGC 3D Tiles specification use to stream massive 3D geospatial datasets (e.g., city models) to a web browser?
- GeoJSON with Z coordinates
- Hierarchical tiled batched 3D model (b3dm) and tileset.json (Correct answer)
- CityGML flat file
- KML with altitude tags
Correct answer: Hierarchical tiled batched 3D model (b3dm) and tileset.json
3D Tiles uses a tileset.json hierarchy with tile formats like b3dm (Batched 3D Model) to stream large 3D city models to clients such as CesiumJS.
Question 4: What is the purpose of an API key in a web mapping service such as Google Maps Platform or Mapbox?
- Encrypting tile images during transmission
- Identifying and authenticating the application to control access and track usage billing (Correct answer)
- Specifying the coordinate system for returned data
- Enabling offline caching of map tiles
Correct answer: Identifying and authenticating the application to control access and track usage billing
API keys authenticate the calling application, allowing the provider to enforce usage quotas, billing, and access restrictions.
Question 5: What is 'map tiling' at zoom level 0 in a standard web map (e.g., OpenStreetMap)?
- The entire world is covered by a single 256×256 pixel tile (Correct answer)
- The world is divided into four equal tiles
- Each continent is one tile
- No tiles exist at zoom level 0; it starts at level 1
Correct answer: The entire world is covered by a single 256×256 pixel tile
At zoom level 0, the entire world is represented by exactly one 256×256 tile; each additional zoom level quadruples the number of tiles.
Question 6: Which JavaScript library is specifically designed for 3D globe and terrain visualization in a web browser, often used for satellite imagery and 3D city models?
- Leaflet
- OpenLayers
- CesiumJS (Correct answer)
- Turf.js
Correct answer: CesiumJS
CesiumJS is an open-source JavaScript library for rendering 3D globes, terrain, imagery, and 3D Tiles in a WebGL-powered browser environment.
Question 7: In the context of web GIS, what does 'server-side rendering' (SSR) of maps refer to?
- The browser uses WebGL to draw map tiles
- The GIS server generates map images and sends pre-rendered graphics to the client (Correct answer)
- Map labels are rendered in a separate thread on the client
- GPS coordinates are processed on a remote server before display
Correct answer: The GIS server generates map images and sends pre-rendered graphics to the client
Server-side rendering means the GIS server (e.g., GeoServer, MapServer) composites and sends pre-drawn map images (as in WMS), offloading rendering from the client.
GIS Web GIS and Services 5
What is the difference between WMS and WMTS in terms of how they serve map images?