Mapping Center Answer:

I know this can be confusing -- you are actually seeing all the points in both displays but they are being drawn with the same size symbol even though the map is at different map scales. To see the point symbols (and in fact, at the same size oh all displays, you need to set what is called a "reference scale". This is a property of the data frame, so to set it, right click the data frame in the Table of Contents and on the General Tab, you can set the reference scale. You want to set this to be the map scale that is the same as what you want to use on the final map -- that way you can see what the symbology will look like when you publish it. An easy way to do this is to set that scale in ArcMap while you are in the page layout view, and then set the properties of the data frame -- that way you can 1) be sure the symbols look right at the final scale, and 2) use the Use Current Scale option when you set the reference scale.