9. Frequently Asked Question
- What are the differences between QGIS Desktop and QGIS Server? - QGIS Desktop has a graphical user interface and allows you to create and modify maps. QGIS Server is a server application serving your QGIS project files to end user applications via OGC web services like WMS, WFS, etc.. 
- What is OGC? - The OGC (Open Geospatial Consortium) is an international not for profit organization committed to making quality open standards for the global geospatial community. 
- Name some other web mapping servers? - ArcGIS server, Geoserver, Mapserver, Mapnik etc. 
- How to compare QGIS server to other web mapping servers? (2021/01/01) - Features - QGIS Server - GeoServer - ArcGIS Server - Since - 2006 - 2001 - 1999 - Licence - GPL - GPL - commercial - Commercial support - Multiple companies - Multiple companies - ESRI and its vendors network - Technology - C++/python - Java - C++ - Tile cache - yes - yes (via GeoWebCache) - yes - 3D - No - No - Yes - Querying - FES (2.0) and OGC (1.0) filters - CQL and OGC filters - OGC filters - Report generation - yes - yes - yes - Server administration - yes via third parties (LizMap, QWC2, etc.) - web + API REST - web + API REST - GIS project Layer/symbology edition - complete via dedicated GUI - simple via web interface - complete via dedicated GUI 
- What are the OGC specification versions implemented in QGIS server compared to other web mapping servers? (2021/01/01) - OGC standards - QGIS Server - GeoServer - ArcGIS Server - WMS (Web Map Service) - 1.3.0 - 1.1.1 - 1.3.0 - 1.1.1 - 1.3.0 - 1.1.1 - WFS (Web Feature Service) - 1.1.0 - 1.0.0 - 2.0.0 - 1.0.0 - 2.0.0 - 1.0.0 - OAPIF (aka WFS3) - 1.0.0 - no - no - WMTS (Web Map Tile Service) - 1.0.0 - 1.0.0 - 1.0.0 - WCS (Web Coverage Service) - 1.0.0 - 2.0.1 - 1.0.0 - 2.0.1 - 1.0.0 - WPS (Web Processing Service) - no - 1.0.0 - 1.0.0 - CSW (Catalogue Service for the Web) - no - 2.0.2 - no - SLD (Styled Layer Descriptor) - yes - yes - yes 
- What is a tile cache? - Maps are often static. As most mapping clients render WMS (Web Map Service) data every time they are queried, this can result in unnecessary processing and increased wait times. - The tile cache optimizes this experience by saving (caching) map images, or tiles, as they are requested, in effect acting as a proxy between client (such as OpenLayers or Google Maps) and server (any WMS-compliant server). As new maps and tiles are requested, QGIS server intercepts these calls and returns pre-rendered tiles if stored, or calls the QGIS engine to render new tiles as necessary. Thus, once tiles are stored, the speed of map rendering increases by many times, creating a much improved user experience. 
- What is PostgreSQL? - PostgreSQL is a powerful, open source object-relational database companion for QGIS. 
- What is PostGIS? - PostGIS is a spatial database extender for PostgreSQL object-relational database. It adds support for geographic objects allowing location queries to be run in SQL.