1.3. Introduction to major open source WebGIS#
WebGIS is composed of four parts, and it can be seen from the name that it includes at least Web and GIS, which involves technical complexity. From the perspective of WebGIS, open source tools can be divided into two categories: component products and full-stack products.
Free and open source software, open specification and open data#
At present, the use and maintenance costs of commercial GIS software are getting higher and higher. For example, a complete set of ESRI ArcGIS software including client and server is priced at about 700,000 yuan. And its sales strategy is that if you buy server-side software, you must buy client-side software. The reason is that since users use their server-side software to publish services, they must use their client-side software to process data. This is far beyond the affordable range for some relatively small WebGIS applications. And many commercial software GIS data and operations are not completely able to convert and share, resulting in some information islands.
But on the opposite side of commercial GIS software is open source GIS. Founded in 1994, OGC is committed to researching and establishing open geographic data interoperability standards, enabling users and developers to interoperate. The International Geospatial Development Foundation (Open Source Geospatial Foundation) was established in February 2006. Its mission is to support the development of open source geographic information software and remote sensing software and promote their wider application, provide organizational, legal and financial assistance for the projects it supports, and promote the development, promotion and popularization of OSGeo Foundation’s standard software based on geographic information and its Interoperability Technology.
Free and open source GIS software#
Free and open source software is a type of computer software that can be classified as both free software and open source software. That is, anyone who is licensed is free to use, copy, research, and modify the software in any way, and its source code is open and shared, so people are encouraged to voluntarily improve the design of the software. Such software is in contrast to commercial software, which is under strict copyright restrictions and whose source code is generally not available to users.
At present, there are many free and open source GIS software including various levels. For example, large desktop GIS includes QGIS and grass GIS. Currently the more popular server-side software includes GeoServer, MapServer and QGIS server, as well as open source GIS database projects such as PostGIS / PostgreSQL spatial database, In addition, there are some open source projects such as data conversion tools (such as GDAL / ogr) and map projection algorithm libraries (such as proj and geotrans). Most of these software are supported by osgeo.
The role of open data#
Open data is a type of data that can be freely used, reused, and redistributed by anyone. Among its limitations, at best, requires attribution and redistribution using a similar protocol. Data.gov contains a lot of open data collected by the U.S. government. In addition, OpenStreetMap (OSM for short) is also a widely used open data source. The OSM project was founded by British Steve Coast. The concept was inspired by the Wikipedia website. It is an online map collaboration project for building free content, the goal is to create a free-content map of the world that can be edited by anyone, with an easy-to-navigate solution for cheap mobile devices.
Components of WebGIS#
Four components of WebGIS: WebGIS Application Development and GIS Services
Web Services and Application Services
Client: The client is where the user interacts with spatial objects and analysis functions in Web GIS. It is also where Internet GIS programs present their output to the user.
Web Servers and Application Servers: Web servers respond to requests from web browsers via HTTP. When the web server passes requests to other programs, it requests services from the application server. The application server acts as a translator or connector between the web server and the GIS server.
GIS server: GIS server is a main component, which can complete spatial query, perform spatial analysis, and generate and provide maps to clients according to user’s request.
Data Servers: Data servers provide spatial and non-spatial data in relational or non-relational database structures. In this website, we pay special attention to GIS server as well as client application. Many GIS servers are on the internet such as GeoServer, MapServer, Mapnik, MapGuide, QGIS Server, etc. All of these servers are open source servers, i.e. freely available. ArcGIS also provides a server, but it is not freely available but has many additional features. All open source servers are free to download from their respective websites.
The following products are typically used as components and combined with other tools in various combinations to create custom applications.
MapServer is an open source platform for publishing spatial data and creating interactive map applications to the Web. It has been around since the mid-1990s and is considered mature and stable, with continued active development. Its main focus is to generate maps from multiple layers, including base imagery and spatial datasets. It also offers smart labels, including advanced typography and layout, including collision detection. It can read and serve spatial data in various formats, including Shapefiles, WMS, GDAL, PostGIS, and GeoTIFF. It is typically used to generate map tiles and its MapCache extension. It has libraries that support application development in various languages, including Python, Perl, Ruby, Java, and PHP.
PostGIS is an extension to the PostgreSQL database that supports spatial queries. PostgreSQL is both a relational and object database and is widely regarded as the most advanced open source database, similar to Oracle and MS-SQL. PostGIS supports various spatial queries including proximity, radius, bounding box, collision/overlap detection, etc. It is a very useful tool that is often used in Web GIS projects.
GDAL (Geospatial Data Abstraction Library)#
GDAL is a translation library for geospatial data formats. It can import and export a wide variety of file and encoding types. It can be used to convert spatial data between different projection systems. Raster data formats are handled by GDAL, and vector data formats are handled by OGR, now included in GDAL. It can also be used to create mosaics from multiple image file sources. GDAL is a valuable tool for taking data from disparate sources and transforming it into collaborative work.
TileMill is a desktop application for generating map tile images, which are then hosted as static files to be used as base layers. TileMill can be used to create visually stunning base layers. It has a strong focus on aesthetics and includes many well thought out presets that enable people without a design background to make very attractive and professional map layers. The development of TileMill is led by a company called MapBox. They offer several attractive paid services, including tile hosting and curated and fine-tuned base layers.
The following products are distributed as “stacks” or “bundles”. They are preconfigured combinations of modular products. Some can be used as is (after adding configuration and base layers), and all of them can be extended further to create custom applications.
GeoServer is mainly based on the Java language. It provides basic functionality for creating and editing geospatial data and providing maps in a service-oriented architecture. It uses the OpenLayers module and provides and implements the Web Map Service (WMS) standard. It also uses the GeoTools framework, which covers a small subset of MapServer’s functionality. Like GeoServer itself, it is written in Java. It will primarily appeal to developers already using Java-based tools and platforms.
GeoDjango is a set of spatial extensions to the Django application framework. Written primarily in Python, Django is one of the most popular general-purpose frameworks for building web applications using Python. Unlike GeoMoose or MapGuide, it does not provide out-of-the-box applications, but a set of carefully designed building blocks for building custom applications. Unlike some of the other stack products described above, it makes fewer assumptions about which other geospatial tools will be used in the stack and provides integration points through a series of clearly designed, well-documented APIs. It may appeal to developers who want more choice and control when building applications and those who prefer the Python language.