GIS and Cartography Workgroup
Aviso Internet Map Server
Introduction: a different kind of WWW content
Images are one of many kinds of media flowing to your PC or mobile device from WWW server somwhere on the net and carrying as various content as graphical WWW page elements, vacation photos and data visualizations. It is tempting to think of maps as of another visual content which can be easily embedded on WWW pages using common image formats like JPG or PNG. However, as cartography proves, maps are more then just images. After many years of GIS experience, it is a commonplace that a number of features essential for mapping cannot be handled with simplistic map=image model. Among them are:
- panning and zooming logic,
- searching logic,
- projection-based display,
- composite nature of maps.
A regular WWW server is not able to satisfy these requirements. Firstly, it has no notion of map "behind" an image. Secondly, there is no widely accepted format to send GIS data to user's WWW browser. The solution must be to merge GIS technology with internet communication.
Architecture of cooperation
A specialized piece of software, called mapping server produces map image in common format and then lets regular WWW server do it's job. Two servers work in close cooperation in both directions. Everything starts with user clicking on a link on WWW page. A request specifying map name and display details flies to WWW server and is immediately forwarded to mapping server. Mapping server renders a map image and passes it back to WWW server. WWW server sends this image to the internet user.
AIMS (Aviso Internet Map Server) is GIS software add-on to regular WWW server. It reads maps data in native GIS vector format and renders map image in JPG or PNG (Portable Network Graphics) format. Map objects are maintained in geographic coordinates. This way AIMS is able to apply projections on the fly and provide smooth panning with continuous relocation of projection center (which is impossible with raster image).
AIMS maps can span huge area, like whole earth, without loss of detail and without exorbitant demand for storage space or transfer bandwidth. As map image is generated on demand, viewing scale can be set to arbitrary value. Zooming implemented this way is free of pixelation effects and holds proper size relations between labels, symbols and background contents. As a bonus of centralized map rendering, all components of graphical appearance like colors, fonts, fill patterns and symbols are guaranteed at all end-user displays.
Maps on pages
To the internet end-user, map image is always a part of complete WWW page. AIMS does not generate pages and relies on whatever is given - any page old or new can serve the purpose, as long as it has a reference link to map. This reference is made of simple line of code embedded within HTML lines.
More demanding web designers can follow the second scenario. Map can be accompanied by extra elements like legend, zooming and panning buttons, current scale indicator and so on.
Read more about extra page elements...
Preparing maps for AIMS
From GIS point of view, AIMS is nothing else than AVISO Geographic Information System with different front-end. AIMS reads AVISO maps with all of cartographic functionality and ways of navigation (consult AVISO page to see what is possible). The only exception is that AIMS will treat the map as static in terms of database access, that is it will not refresh the contents from the database. This attitude leads to very straightforward workflow based on "single file" principle.
Map editor prepares a map using available data and sets the geographic limits, scale range and discrete scale values available to the end user. Map file is handed to map server administrator or copied into public AIMS folder. No re-formatting, re-linking or any other operation is necessary except for copying.
Gazetteer is an index of geographic names with their coordinates used for searching text information on maps.
Gazetter module is built into AIMS and seamlessly connected to map navigation and page processing. In reaction to a search keyword, AIMS returns a list of matching names as clickable links. Links follow to the new page with map centered on retrieved geographical position. The links list may be combined with map and page content in many ways. Read more...
AIMS supports multiple gazetteers loaded at the same time. Also, arbitrary cross-links between gazetteers and maps are possible because gazetteer content is independent from any map (a name found in gazetteer does not need to be a label on map). As a consequence, one gazetteer may serve many maps.
Gazetter files are prepared in AVISO from database tables. Except for the names they may include additional explanatory column (eg. administrative unit). Text is stored in Unicode standard and displayed in native language, but the search is neutral to diacritic marks to make life easier to foregin visitors.
AIMS is designed to work in cooperation with IIS (Internet Information Services) which is a part of Microsoft Windows™ Server platform. A small part of AIMS is a module loadad into IIS (so called IIS extension). The map server proper is a separate Windows Service.
Part 1 "Anatomy of AIMS communication"