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Added Basemap changes data frame's coordinate system

Question asked by Vicky14 on Jul 15, 2014



I am working on exercise 8a and I came across something that happened also during exercise 6a.


A. Exerc, 8a.:  I have added LARiver onto the map (from ReadyData.gdb) and therefore the coordinate system of the data frame is California State Plane Zone 5. Then I added  the "Terrain with Labels" basemap and then I checked the data frame's coordinate system. To my surprise it was changed to the geographic coordinate system of the basemap which is  WGS84 Web Mercator. Why did this happen since according to Lesson 3 (but also to Lesson 5, page 176) the first layer added to the data frame set the data frame's coordinate system?


Do I have to change now the WGS84 Web Mercator into NAD83 (as it was done during Lesson 5, page 177) in order to move on with Exerc,8?


B. Exerc. 6a: I came across the same issue while I was doing also this exercise. After I had created ProximityZone layer, I moved on with adding the Topographic basemap. At that moment I had not yet realised that my data frame's coordinate system was changed to WGS84, but when I added the BlockGroups to the map (see page 207) I got a Geographic Systems Warning which did not make sense to me since all layers in ReadyData.gdb were set to California State  Plane Zone 5. I checked then the data frame's  coordinate system and I saw  that  it was changed to WGS84.

( I did not change the data frame's coordinate system during this exercise, I simply moved on with the rest of the exercise).


(I have ArcMap 10.1 version).


Best regards,