GIS Web GIS and Services 3 — Questions and Answers
Question 1: In the context of web mapping, what is a 'bounding box' (BBOX) parameter used for in WMS requests?
- Specifying the coordinate reference system
- Defining the geographic extent of the requested map image (Correct answer)
- Setting the output image resolution in DPI
- Listing available layer names
Correct answer: Defining the geographic extent of the requested map image
The BBOX parameter defines the spatial extent (minX,minY,maxX,maxY) of the map area to be returned by a WMS GetMap request.
Question 2: What is Mapbox GL JS primarily designed to do?
- Edit shapefiles in a desktop environment
- Render interactive vector tile maps in a web browser using WebGL (Correct answer)
- Process raster imagery on a server
- Generate PDF map exports
Correct answer: Render interactive vector tile maps in a web browser using WebGL
Mapbox GL JS is a JavaScript library that uses WebGL to render customizable, interactive vector tile maps directly in the browser.
Question 3: Which protocol is commonly used to stream real-time geographic features to a web map as they are updated?
- FTP
- WebSockets or Server-Sent Events (SSE) (Correct answer)
- SMTP
- NTP
Correct answer: WebSockets or Server-Sent Events (SSE)
WebSockets and SSE provide persistent connections that allow a server to push real-time feature updates to a web mapping client without polling.
Question 4: What is the role of a spatial index (e.g., R-tree) in a web GIS database?
- Storing attribute data in alphabetical order
- Accelerating spatial queries by organizing geometries by bounding box (Correct answer)
- Converting coordinates between projections
- Compressing raster images for faster download
Correct answer: Accelerating spatial queries by organizing geometries by bounding box
Spatial indexes like R-trees organize geometries so the database can quickly discard regions that don't intersect a query envelope, dramatically speeding up spatial queries.
Question 5: In ArcGIS REST API, what does querying a Feature Service with 'where=1=1' accomplish?
- Returns no features
- Returns all features in the layer (Correct answer)
- Returns only the first feature
- Triggers a server-side geoprocessing task
Correct answer: Returns all features in the layer
The SQL expression '1=1' is always true, so it matches every record in the layer, effectively returning all features.
Question 6: Which open-source JavaScript library is known for its lightweight footprint and is widely used for creating mobile-friendly interactive maps?
- OpenLayers
- Leaflet (Correct answer)
- Cesium
- D3.js
Correct answer: Leaflet
Leaflet is a popular, lightweight (~42 KB) open-source JavaScript library optimized for mobile-friendly interactive mapping.
Question 7: What is the purpose of the SRS (Spatial Reference System) parameter in a WMS GetMap request?
- Specifying the output file format
- Defining the coordinate reference system for the returned map image (Correct answer)
- Setting the number of layers to display
- Controlling the image compression level
Correct answer: Defining the coordinate reference system for the returned map image
The SRS (or CRS in WMS 1.3.0) parameter tells the server which coordinate reference system to use when rendering the requested map extent.
GIS Web GIS and Services 3
In the context of web mapping, what is a 'bounding box' (BBOX) parameter used for in WMS requests?