Problem: Switching between the data view and the layout view changes the scale of the data frame
When changing between the data view and the layout view, the scale of the map changes slightly.
The scale in the data view shows a value appropriate to the data display size but is not dependent on a page size. The data frame is not currently being restrained to the size of a printer. In the data view, the map will display at the same scale regardless of the desired page size. The scale value in the layout view is dependent on a particular page size. The size of the data frame will adjust to fit the constraints of that page and may adjust the scale. The difference in scale will be proportionate to the size of the page selected.
Solution or Workaround
Use the fixed scale option in the Data Frame Properties to avoid this scale change.
B. Select Properties.
C. Click the Data Frame tab.
D. Change the Extent radio button to Fixed Scale.
E. Enter the desired value if your map is not already set to that display value.
F. Click OK.
Alternatively, use the Fixed Extent option, but note that changes in the page size or data frame size may change the scale.