Certain GIS layers appear, then when I zoom in or out they will disappear. What is going on?
There are a lot of GIS layers that can become visible or not visible depending on the scale of the map. An example of this process is the Parcel layer. It will only be available/visible to turn on only when you are zoomed in fairly close and as you zoom out it will turn off automatically. This has been purposefully set up to optimize bandwidth the viewing of the most popular GIS layers at a given scale. UPDATED!