How to speed-up Dynamic Map services?

Question

I am working on a ESRI Flex based application that will display data from a Dynamic Map Service. It need to be Dynamic, since the end user should have the option to turn on & off layers. This is possible only with Dynamic Map services & not Tiled map services.

What are some of the steps that can be taken to increase the speed with which tiles are sent to the client by the server?

I am looking at ESRI's Dynamic Maps available on ArcGIS online, and they are quite fast. Any idea on how they get such good performance?

Answer 1

I would assume that you would just like for any live web map service, you make your map server 'think' as little as possible. In other words, pre-compute everything that you can.

1. Put all of your data in the same SRS so there is no projection happening 'on-the-fly'.
2. Create spatial indexes on your data.
3. Build generalized overviews of your data and use scale dependency to select the appropriate layer for a particular scale. (e.g. it makes no sense to draw a poly with 10,000 vertices if the output image is only 250 x 250 pixels.)

Answer 2

You may have already done this but it's worth mentioning for others that might come along. Spending some time using the Map Service Publishing toolbar in ArcMap can make a world of difference in the performance of a dynamic map service. The Analyze Map tool works well for finding issues that slow down map services. Also, saving and publishing as a map service definition (MSD) rather than an MXD allows for significant performance increases.

Some links:

• Publishing Optimized Map Services
• Authoring and Publishing Optimized Map Services Online Seminar

Answer 3

A few other points to add to DavidF's answer:

• If you can, make sure to use an optimized (MSD) based service. They do draw faster than a regular (MXD) service, and the process of creating the MSD service will run some analysis on your map which can expose issues that could lead to slow draw times.

• Use simplified renderers where possible. Avoid complex drawing operations like dithering, color gradients, and raster markers.

• Use the minimum amount of data that satisfies your business requirements. If you have attributes in your data that will not be used for drawing the map, remove them. Even if you do need to report on the data, you can obtain it as required from the client (although this adds extra programming work)

• Turn on verbose logging for your map and review the log files to see what ArcGIS Server does when you draw a map. Instructions for configuring verbose logging are on Esri's blogs site. That's for version 9.3, but the config location is the same for ArcGIS 10.

Remember, tuning is a very specific operation that is very subjective and specific to what you are doing; comparing the performance of your own map with itself will be more valuable than comparing your performance to someone else's.