I have a map document file (.mxd) with a size of 0.3 MB. I also have two layer files (.lyr), containing large rasters. Together they are 16.2 MB. If I add the two layer files to my map document in ArcMap and save, it becomes 16.5 MB large.

This leads me to believe that all the data in the layer files are duplicated in the map document file. Is that so? If not, what causes the map document to swell? Is there any way to avoid this, since I want to keep the size of my map document low?

The layer files will be used in many map documents, and storing the rasters over and over again seems rather unnecessary.

  • Layer files don't store the raster itself, they don't contain any actual geographic data, only a reference to the data along with some properties about how to render it (properties for symbology, labeling, etc.). You can have a proper explaination here: gis.stackexchange.com/questions/54111/…
    – Vale
    Aug 7 '15 at 13:44
  • Thanks for the reply! I am a bit surprised that the layer files are 16.2 MB then. Might be because there are 100+ tiff files in each layer. So I guess I should merge the rasters and the layer files will become smaller.
    – Anders
    Aug 7 '15 at 13:49

A layer (.lyr) file and your rasters are not the same thing. A layer (.lyr) file is serving two functions:

  • It tells ArcMap where to find the raster data.
  • It tells ArcMap how to draw the raster data.

A layer file by itself can be shared between multiple users. When brought into ArcMap, this information is stored in the map document, along with any changes made to how the information is displayed.

In other words, the layer file is essentially being duplicated, not the data it's pointing to.

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