The first layer you add to a map is considered to be the basemap layer. It dictates the overall spatial reference of a map. Any tiled layers you subsequently add to a map must also be in this spatial reference, otherwise their content will not be displayed. Dynamic layers, on the other hand, can be in any spatial reference. They will automatically re-project their content, if necessary, into the map's spatial reference.
I have been consuming GIS resources for a while, so far I could get things done without knowing too much of GIS tech data. Please be easy on me if its so obvious.
Some mapservices dont have a spatial reference Example . As of now when user tries to add a map layer, I was validating if it has a spatial reference. Is that the proper way of validation?
Please give a proper explanation.