Friday, March 5, 2010

Caching in ArcGIS Server

In our efforts to get an online map up and running I have created an ArcGIS Server service showing aerial imagery. I started creating cache tiles at about 10:30am this morning (3-5-2010). The scale levels I am creating tiles for range from 1:1,000 down to (or should it be up to? scales are whacked) 1:512,000. There will be an additional scale of 1:500, but I chose not to cache that scale initially. I will do an update on the cache later based on a feature class in the Snyderville Basin and do "on demand caching" at that scale for the rest of the county.

For those who don't know what a cache is, or ArcGIS Server for that matter, here is a short (hopefully) explanation. However, if you don't know what either of those are, you probably wouldn't be reading this far into this posting anyway.

ArcGIS Server is software that serves geographic services (data, maps, geographic processing) on the web. My aerial photo service shows various aerial fly-overs that the county has acquired over the past few years. If I were to put the service on the web without caching the service, each time a user changes zoom levels or centered the map on a different area, the server would have to render the images and send them back to the user's browser. With a cached service the images are already created on 512 x 512 pixel jpeg tiles at the various scales, so the server only has to return the tiles that the user needs. This way there is less server processing and the experience is faster for the user. If you have spent any time on any of the online mapping programs, you have probably noticed the cached tiles drop into the browser square by square. The tiles are created at certain scale levels with corresponding detail level as you zoom in.