The Gallery section of the Maps area provides finalized maps. This Library section provides the components that are used in the final maps.
Bookmarks are the "places" in mapping. A spatial bookmark identifies a particular geographic location that you want to save and reference later. For example, you might create a spatial bookmark that identifies a study area. As you pan and zoom around your map, you can easily return to the study area by accessing the bookmark.
Expressions are statements that determine label text. Label expressions typically concatenate or modify the contents of one or more fields, and may add additional text strings to create more informative labels. They can contain Visual Basic script or JScript to add logic, text processing, and formatting for the labels.
Layers are "pages" of information and usually a map will contain multiple layers. Each layer may hold any portion of the maps content (e.g. symbology, data source pointer), and layers may be made visible or invisible, showing or hiding their contained objects, in any combination. They may also be rearranged in terms of relative "stacking order".
Map Files are the original maps (.mxd) and require GIS software to view and change.
Scripts (e.g. Python) help automate map manipulation.
Styles are a collection of predefined colors, symbols, properties of symbols, and map elements that allow a mapping standard to be followed and help promote consistency in mapping products.
Styles help define not only how data is drawn but also the appearance and placement of map elements and other cartographic additions on a map. Every time a particular map element or symbol is chosen and applied, the contents of a style is being used.
Benefits of using styles include
Symbols are the graphics used to represent a geographic feature or class of features. Symbols can look like what they represent (trees, railroads, houses), or they can be abstract shapes (points, lines, polygons) or characters. Symbols are usually explained in a map legend.