[OpenLayers-Users] GIS Data Access to Maps

[Phil Scadden]

Adding Alex's comments - on a browser you have a number of important 
limitations to consider. The first is bandwidth - you have download both 
the js code and data you are going to display. Furthermore the data 
generally needs to be an ascii format so you lose indexing and have to 
contend with bulky representation of data. The second is javascript 
itself. While a lot of work has been done to improve it, it remains an 
interpretated, single-threaded language with all kind of limitations 
when it comes processing. Openlayers supports geojson, gml, kml (not kmz 
though) but in practise, dealing with a feature set with more than 500 
bits of geometry gets very slow.

For all the improvement in html5, the old mantra of do what can on the 
server still applies. To this end, what make web mapping hum is WMS/WFS 
servers (eg Geoserver, mapserver, ESRI arcGISServer). You load your GIS 
sets onto these servers and talk to them via openlayers with WMS/WFS 
protocols. For WMS, the client requests a map of a particular area and 
the server renders your GIS data and sends it back in image format. For 
WFS, you make a query and get the features back in say GML and render on 
the client.  (so you make sure the application only make requests for 
small data sets).

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