About working with layers
A web map is composed of a basemap of reference geography and one or more layers of data above it. Some properties of a layer are always available. For example, you can always view a description of the data in the layer, rename a layer, or change its transparency. Other properties are controlled by the author of the layer. As a web map author, for example, you decide whether or not users can resymbolize or edit features and if you want to create an interactive filter of the feature data. You can also save the item properties back to the item. Once you add a layer to a web map, even if you didn't author the layer, you have some control over its appearance. For example, if the layer contains symbols, you can change how they are displayed and set their visibility range. If the layer contains feature data, you can view the attribute information in pop-up windows or as a table. You can also organize the order of the layers.