Web GIS

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The term Web GIS is generally understood to mean a GIS application whose core functions rely on web services ( geospatial services ) that are specialized for spatial data . A web application specializing in geodata or a geobrowser can be used as the graphical user interface .

The terms GIS online , Internet GIS , NetGIS , Distributed GIS or Internet Mapping are often used synonymously . Internet mapping - the general term - can only be understood as the retrieval of geodata from the Internet in a desktop GIS. If at least two programs exchange geodata over a network ( client-server principle), one can speak of a web GIS. Usually, however, the exchange of geospatial data is meant via network protocol , specifically via HTTP .

It makes sense to distinguish between different types of web GIS. Brandon Plewe made a very early subdivision . Some types should now be presented here.

These differ mainly in the functionality provided by the server computer and the client computer. With a typical desktop GIS, the entire GIS functionality and the data are available on a client computer. With modern free web GIS architectures with geospatial services such as deegree , GeoServer or the UMN MapServer in connection with a web browser as a client, the functionality of the client is mostly based on visualization and trivial GIS functions ( movement in the map , zoom , distance measurement etc.), while the main workload lies with one or more servers (Distributed GIS ie S.). A web browser is required as a user client.

Spatial data server

In this case, a desktop GIS has the option of loading data from remote computers and processing them locally. The computer that provides the geodata for downloading is called the geodata server. Research options are necessary for the selection of the geodata. The task of creating maps remains with the client, which based on its functionality can therefore be referred to as a thick client .

Map server

Static map server

Here, the task of creating maps lies with the server, but more precisely this does not have to be understood as the dynamic creation of a map. So-called "static maps" are widespread, in which the raster image of a map is offered, such as for example route sketches or the like. Numerous maps are also offered on the Internet using the HTML technology of the imagemaps , which give the user the opportunity to take a closer look at a specific map section. The card is also static, but the client (as in the other examples) only needs limited functionality (“thin client”).

Dynamic map server

The cards are generated and returned dynamically on request by the client. The server evaluates the request and transmits the relevant information to a map generator. On the one hand, this is limited to the different forms of representation (e.g. color, symbols), on the other hand, topic-related selection options ( layers ) can also be available (online information systems). Here the request is processed on the server side, the requested section is selected from the available data and a map is produced.

From this subdivision, it is important to differentiate between the terms client / server and map client / map server. So far, the technical side of the Internet client and the Internet server have been spoken of. A distinction was made as to whether the client had to provide a lot of functionality (thick client) or little (thin client). If you work in the terms of map server and map client, it must be noted that you cannot do without a suitable map client when working on a map server as described above. This is usually a website that e.g. B. provides the functions of layer selection, displays the map image and offers the various navigation options (panning / movement, zoom). The map client is a link between the Internet client, or better user, and the map server. It can either be offered by the operator of the map server himself or it is an external map client that can communicate with the map server. The functionality is by no means up to the user, who can still be described as "thin", since the entire functionality can be accessed via a normal web browser.

Online GIS

On the server side, the functionality of a GIS is accessed so that more complex GIS functions (e.g. buffers ) are possible. In detail, communication takes place as follows: The client sends a request to an HTTP server (e.g. Apache , Microsoft - IIS ...) via an Internet protocol , which forwards this request to a GIS interface. As a result, the request can be further evaluated for GIS-specific commands, which are forwarded to an underlying GIS. There then a) these commands are interpreted, b) the data are accessed, c) these are processed with various analysis scripts and finally d) a map (report) is created. The card is returned to the GIS-interface, in which case the the transmission to the HTTP server response (the response) can be completed to the client based on the Internet Protocol. A geoportal is a specific version of a web GIS in which the web browser is used as a client.

The existing OGC-compliant geospatial services are a special case of online GIS. The interfaces specified by the OGC make use of far greater possibilities of a distributed GIS than has been shown in previous cases. The basis for this is the standardization of communication between the different systems. The previous rigid distinctions between client and server no longer offer a sufficient form of representation. Rather, a client (the user) is still present, but this accesses a server system in which, however, one server can in turn be the client of another server. The data no longer only has to be on one computer, but is in the network separately from the computers with GIS functionality. Furthermore, not only one computer with GIS functionality is addressed, but many computers can provide different functionalities (services). The file format must be readable and writable by all service providers so that they can be exchanged with one another.

An example may serve as an illustration: The data is available on any number of computers in the different coordinate systems and in the different file formats. In order for a user to be able to generate a map from these sources, one or more services for converting files into a generally readable format must first be available, and secondly a service (or more) that can transform between different coordinate systems. At the end of these different services there is finally the geospatial service (e.g. Web Map Service ), which generates the map image and returns it to the user. The OGC has already passed some specifications of these services as interfaces, some more are still in the discussion stage. Of course, these three mentioned services alone are not sufficient to display a map. But the interaction already shows - from the selection of the data via a metadata catalog, to data access, via the coordinate transformation to the character rules, to visualization - that there is a great deal of complexity when it comes to the order in which these services have to be processed: When is the coordinate transformation initiated, when do the file formats have to be converted?

SensorGIS

Under SensorGIS means the combination of Web GIS, wireless sensor networks and remote data transmission. It is an initiative of the OGC ( Open Geospatial Consortium ), which aims to encourage its members to develop projects linked to GIS.

Web links

Individual evidence

  1. ↑ Brandon Plewe: GIS Online - Information retrieval, mapping and the Internet . OnWord Press, 1997, ISBN 1-56690-137-5 .