Problem: The map scale does not change when changing the image size of an ArcMap Server GET_LAYOUT request
When you change the width and height of the layout output such that it is different than the page size set in the ArcMap document, the absolute map scale does not adjust accordingly, it will not change. The absolute scale (scale text) will be incorrect.
Note: The scale bar will be correct, however.
When exporting an ArcMap Service layout to an image output type (bmp, jpg, or png) you can change the image size of the layout output by changing the width and height attributes of the IMAGESIZE tag. Doing this is similar to taking a map and increasing or decreasing the size of the map using a copier.
ArcMap Server will not adjust the scale to match the new size of the layout. The scale will always be based on the page size set in the layout of the original ArcMap document.
Solution or Workaround
If you want the absolute scale to be correct you must set the image size of image output type to equal the actual page layout set in ArcMap.
The IMAGESIZE tag of a GET_LAYOUT request consists of three attributes: dpi, width and height. IMAGESIZE affects the quality of the output. It also determines the size in pixels of image format output (bmp, jpg, png, or gif). Output in vector format (ai, emf, eps, pdf, or svg) is determined by the page size of the original ArcMap layout.
For more information please refer to the ArcXML Programmer's Reference Guide topic "Using GET_LAYOUT and LAYOUT with ArcMap Image Services".
The use of IMAGESIZE attributes depends on the output format being used.
For image format output (bmp, jpg, png, gif):
Width and height are required (the dpi setting will be ignored for image format output).
If no width and height are specified the following warning is printed into the log file: "Width and Height are not found in IMAGESIZE tag. Use default." The default is calculated based on the page size of the ArcMap layout and the default dpi of 96.
In order to maintain the proper map scale, width and height may be modified in order to maintain the aspect ratio present in the ArcMap layout.
For vector format output (ai, emf, eps, pdf, or svg):
DPI can be used to increase the quality of vector format output. If DPI is not specified in the IMAGESIZE tag the default value is used and the following warning is printed into the log file: "DPI is not found in IMAGESIZE tag. Use default."
The attributes width and height will be ignored. The size will be taken from the page size of the ArcMap layout.
When autoresize (an attribute of the GET_LAYOUT tag) is set to true and the layout with modified width and height is larger than the maximum image memory limit, the layout will be reduced to a size smaller than the Image Memory limit. The reduced image will also maintain the height/width ratio.