GIS - Geographic Information System Web GIS and Services Questions and Answers — Questions and Answers
Question 1: An organization is deploying a public-facing web map that will display frequently changing data, such as real-time vehicle locations and operational statuses. Users must be able to click on individual features to get the latest attribute data. Which OGC web service standard is specifically designed to serve vector feature geometry and attributes that can be queried and manipulated by the client application?
- Web Map Service (WMS)
- Web Coverage Service (WCS)
- Web Feature Service (WFS) (Correct answer)
- Web Map Tile Service (WMTS)
Correct answer: Web Feature Service (WFS)
A Web Feature Service (WFS) is the correct standard because it provides raw vector feature data, including both geometry and attributes, to the client. This allows for rich client-side interaction, querying, and even editing, which is ideal for dynamic data. WMS and WMTS return pre-rendered images (or tiles), not the actual feature data, and WCS is designed for serving raster/coverage data like elevation models.
Question 2: A municipal government wants to provide its high-resolution Digital Elevation Model (DEM) data to engineering firms. The firms need access to the actual cell values for hydrological analysis, not just a shaded relief image. Which OGC service standard is most appropriate for disseminating this type of gridded raster data?
- Web Map Tile Service (WMTS)
- Web Coverage Service (WCS) (Correct answer)
- Web Feature Service (WFS)
- Web Processing Service (WPS)
Correct answer: Web Coverage Service (WCS)
The Web Coverage Service (WCS) is specifically designed to serve and retrieve raw raster data, referred to as 'coverages'. It allows clients to request the actual data values (e.g., elevation values from a DEM) for a specified extent, making it ideal for analysis. WMS and WMTS provide images, WFS handles vector data, and WPS is for executing geoprocessing tasks.
Question 3: A GIS department has created a complex wildfire risk model that analyzes multiple input layers (e.g., slope, vegetation, weather). They need to make this model available through a web application, allowing users to define an area of interest and receive a calculated risk map as output. Which type of web service is designed to expose such server-side analytical capabilities?
- A Feature Service
- A Geocoding Service
- A Tiled Map Service
- A Geoprocessing Service (Correct answer)
Correct answer: A Geoprocessing Service
A Geoprocessing Service (or OGC Web Processing Service - WPS) is designed to expose geoprocessing tools and models over the web. It allows a client application to send input parameters to a server, which then executes the analysis and returns the results (such as a risk map or summary statistics), without the client needing to perform the complex computation.
Question 4: Which of the following is the primary advantage of using a cached or tiled map service (like WMTS) for basemap layers in a high-traffic web mapping application?
- It ensures the client always receives the most up-to-the-minute data.
- It allows for complex, on-the-fly attribute queries of the basemap features.
- It significantly improves performance and scalability by serving pre-rendered map images. (Correct answer)
- It enables client-side editing of the basemap geometry.
Correct answer: It significantly improves performance and scalability by serving pre-rendered map images.
The main benefit of a tiled map service is performance. The server pre-renders the map at various scales and stores the images as a cache of tiles. When a user requests a map, the server simply sends the appropriate stored tiles, which is much faster and less computationally intensive than drawing the map dynamically for every request. This makes the application faster for the user and more scalable for the provider.
Question 5: A developer is building a web application using a RESTful API to interact with a GIS server. Which statement best describes the core principle of this architectural style?
- It requires a persistent, stateful connection between the client and server for all interactions.
- It uses a single, complex URL endpoint to handle all possible requests, differentiating them with XML-based commands.
- It treats all server resources, such as maps and feature layers, as uniquely addressable via URLs and uses standard HTTP methods (GET, POST, etc.) to interact with them. (Correct answer)
- It relies on proprietary communication protocols to ensure high performance and security.
Correct answer: It treats all server resources, such as maps and feature layers, as uniquely addressable via URLs and uses standard HTTP methods (GET, POST, etc.) to interact with them.
The core principle of REST (Representational State Transfer) is that resources (like a map service or a specific feature) are identified by unique URLs. Clients interact with these resources using the standard, stateless verbs of the HTTP protocol, such as GET (to retrieve), POST (to create), PUT (to update), and DELETE (to remove). This makes the API open, scalable, and easy to integrate with various web clients.
Question 6: A web client needs to display a map image from a GIS server. The client sends a request to a WMS endpoint that specifies the desired layers, styles, bounding box, and image dimensions. What will the WMS server send back in response?
- A stream of GML or GeoJSON containing the vector data for the requested features.
- A static image file (e.g., PNG or JPEG) representing a map of the requested area. (Correct answer)
- A metadata document in XML format describing the available datasets.
- The raw pixel values from a requested raster dataset.
Correct answer: A static image file (e.g., PNG or JPEG) representing a map of the requested area.
A Web Map Service (WMS) responds to a `GetMap` request by rendering the requested geospatial data on the server and returning a georeferenced map image (such as a PNG, GIF, or JPEG) to the client. It does not send the raw vector (WFS) or raster (WCS) data itself, but rather a visual representation of it.
GIS - Geographic Information System Web GIS and Services Questions and Answers
An organization is deploying a public-facing web map that will display frequently changing data, such as real-time vehicle locations and operational statuses.
Users must be able to click on individual features to get the latest attribute data.
Which OGC web service standard is specifically designed to serve vector feature geometry and attributes that can be queried and manipulated by the client application?