Maps and Whereness - Ubiquitous Positioning - page 144

8.3.6 The Geoweb, Web 2.0, and AJAX
Simple raster image maps have been available since the early days of the Web.
When a request was made by a user for a map of a particular sort, the GIS behind
the server would create a raster image file (or bring it out of a cache if already
created) and serve it as a simple image. While this approach is still used, the idea
behind Web 2.0 is more complex but far more useful to the user and less wasteful
of computing resources at the host. Rather than sending a single raster map, the
modern approach is to send metadata from which the required map may be created
within the software associated with the user's browser. Metadata includes scripts
that are similar to computer code but is usually in an easily readable textual
format. The script can be interpreted locally in the browser and may then interact
with the normal browser's user controls and other media served within the
metadata. Thus a map may be zoomed, panned, or otherwise changed locally
without the need for the server to keep generating new map tiles.
The metadata is also available via an application programmable interface
(API) so that third parties can use it as part of a more extensive application. The
term “mashup” is used for this approach of combining information from different
providers. Access to the API may be free but normally requires the use of a
registered electronic code key.
Maps are thus served in chunks with everything the user might need included
but only displayed when required under control of the script and controls. The
current name for this approach is asymmetric javascript and XML (AJAX) [17].
The term “asymmetric” covers the idea that the sessions are infrequent compared
with user interaction. “Javascript” is a standard used within many Web
applications that is similar in syntax to the common Java programming language.
The Javascript is not the same as a Java applet, however. An applet is a small
program that runs locally within a controlled environment whereas the script
controls entities already present within the browser environment. Figure 8.2
illustrates AJAX and its efficiency advantages over the original approach.
The concept of running a local map application is particularly useful for
mobile users with mobile Internet connections and local positioning systems that
may sporadically connect to the server. Fragments of map may thus be
downloaded (triggered by location) but used continuously with local real-time
sensed information overlaid.
8.3.7 Tips and Tools for Electronic Cartography
Mapping Hacks [18] is an excellent book for the technically minded that explains
electronic cartography very well and has 100 worked examples of digital mapping
applications that can be followed with moderate computing skills. It covers
mapping of one's life, neighborhood, the world, the Web, and mapping with
gadgets such as GPS receivers, desktop applications, names and places, other
people, and the Geoweb.