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3.] Functionality of an Internet-GIS
For the demarcation of typical functionality of Internet-GIS
roughly the following 5 groups can be formed:
— Static maps
— Dynamic maps
— Editors
— Complete Internet-GIS
— Data management servers
Static maps often come along as so-called clickable maps. By
skillful linking of different pre-prepared maps, also in different
scales, already quite suitable effects can be reached. Such a
solution delivers the linkage of thematic data with simple
navigation/visualisation functionality such as zoom and pan.
Special forms are so-called tiled maps, where a larger map area
is divided into individual tiles, which are linked together by
hyperlinks. Both solutions present raster data, which are
statically prepared in advance and can not be adapted to the
demands of the users on-the fly. Tools for the generation and
publication of clickable maps are available already for many
usual GI systems. An example is the HTML-ImageMapper of
Alta4 for ArcView, allowing to produce already quite useful
solutions. This kind of Internet maps is more or less a standard,
but because of its limited functionality and dynamics it should
not be called an Internet-GIS. Everything the user sees, has to
be physically presented and generated before. The expenditure
for the care, maintenance, and extension is accordingly large.
Dynamic maps represent the next stage. These are characterized
by the fact that the maps are generated from an existing amount
of data based on an inquiry from a client. This volume of data
may consist of vector or raster data. In the result raster data are
often delivered, but also, solutions, which generate vector data
dynamically e.g. in the SVG format, are found. By default the
following functionality belongs to such systems:
— Reference Map as overview map
— Zoom and pan
— Queries from thematically data over map elements
— Object search based on thematic data inquiries
— Export of graphics
— Measure in the map
— Display from position and end-to-end measurement
Technically the dynamic maps are often realised by a
MapServer program. The solution can be used ideally as
information desk system because of its excellent speed and
minimum requirements at the client side.
If updating of the data has to be made or more extensive GIS
analysis functions to be added, another extended form of the
Internet-GIS is to be used or the Map Server solution must be
extended by additional programming effort. The Map Server of
the UMN is a typical representative from the Open Source
range, which is well suitable for the dynamic map production. It
can be extended with additional functions and is programmable.
With the help of provided script languages full-functional
Internet-GIS can be developed from Map Servers.
Functionalities, which go beyond the functions usual Map
Server GIS offer, is represented in the following list:
— Spatial query polygon
— Measurement of area sizes
— Print function
— Export of attribute information
— Export of the geo data
— Next neighbourhood search
— Map annotation
— Thematic classification
143
— Routing/Shortest path
— 3D visualisation
If only semantic data has to be changed and no graphic display
is necessary, e.g. for the change of postal addresses or the
updating of the digital cadastral data, simple editor functions for
data bases, using SQL, are sufficient. These are realised usually
on top of web data base clients or via form-supported solutions.
For adding or editing map elements a graphic component is
necessary and the actualization of the data sets is no longer
trivial. This belongs rather to the group of the full-functional
Internet-GIS.
Due to its special position the terminal server solution will be
pointed out still here. Thereby a stand alone GIS is only
connected by the periphery with the Client. Terminals servers
are based on server based computing. Well-known solutions are
Windows terminals server and Citrix. Thus no new
development of GIS functionality or Internet compatibility is
needed.
In addition software solutions such as data management servers
should be added in the list of Internet-GIS architectures. These
partially deliver similar components as the previously
mentioned groups, but because of its special architecture this
group should be regarded separate. The following
functionalities are offered by (geo)data management servers:
— Overview of spatial, thematic and temporal properties
of the data sets as well as the available functionality.
— Data retrieval making use of a thesaurus and gazetteer
— Export of metadata related to the indicated view, layer
or object in the representation.
— Generalization of metadata, geodata and thematic data
sets for different levels of detail and different users.
— Support of open standards.
— User-referred hints for actualization of large volume
of data.
— Subscription functions and newsletter.
— Wide area cross-linking.
New standards, developed by the OGC, allow to combine the
different solutions described here. For the user in future it will
be no longer evident, which type of Internet-GIS solution is
serving the individual applications.
3.2 Internet-GIS technologies
Depending upon the requirements at the data (extent, quality,
topicality) and the functionality of the application different
expenditure for the development is necessary. One has to
consider the costs of the software, hardware and their
maintenance as well as of the qualified technical personnel.
Simple information systems can already be realised with minor
effort. The most simple form is the representation of static maps
in HTML-pages, which are connected with the pertinent actual
data simply by clicking in the web surface. The next stage is the
realisation of an application as Web. server, also named Web
Mapping (Herrmann/Asche, 2001). The maps are generated
upon request on the server side. Here script-languages are used
such as ASP, PHP or CGI. More fastidious applications with
functionality on the client-side are developed with Javascript,
Java, Flash and/or SVG, relatively low-priced or free
supplementary product lines. Pre-condition is an existing GIS,
in which the data must be regenerated accordingly. The data
presented in the internet-GIS do have the topicality of the
supply in application. Hardly additional requirement are placed
against the Web server and client here.
