What makes a MXD file size larger and how to decrease its size?

I've seen similar complaints on the Esri discussion forums and a quick search turned up this thread. Some suggestions:

• Save a copy of the mxd
• Open the geoprocessing results window and delete the history
• Under geoprocessing options, results management, change the value to a day or two

I maintain several PLTS Atlas projects with north of 80 layouts per MXD. I have long paths as well as complex labeling and complex layer symbolization.

The easiest solution I've found to get the file sizes down and improve performance is to use the "Save a copy" function.

I've learned the hard way that the Defrag tool will re-path/disconnect features that are stored in an SDE database. -Karl

To shrink your ArcMap document, run the doc defrag tool found under your ArcGIS Installation folder: C:\Program Files (x86)\ArcGIS\Desktop10.1\Tools. It also exists at 10.0 as well. I'm not sure if it exists at 9.31. It's been a long time since I used that version.

As mentioned above, geoprocessing history can cause the GP task results at 10.1 can cause the mxds to balloon up, and this was a bug during Beta of 10.1.

I agree that layer symbology definition can effect file size. I have seen this myself were a really complex layer can increase the file size.

From support.esri.com:

Map documents (.mxd files) are compound files. The information describing the map, layout, and any embedded objects saved in the map is organized into units called storages and streams. When you save a compound file, the streams can become fragmented in a process that is analogous to hard disk fragmentation. This can make the map document larger, though it does not increase the likelihood of the document becoming corrupted. The more times you save a map, the more chance that fragmentation will make the document larger.

You can also find information here: http://support.esri.com/en/knowledgebase/techarticles/detail/33187

Hope this helps you out.