Please refer to the Web map specification topic for an updated version of the web map specification.
The web map item information contains a title, description, and other metadata used to advertise an ArcGIS web map in a client application such as ArcGIS.com or your own organization's portal.
For item information JSON syntax, see the Item documentation in the ArcGIS Portal API reference.
If you are a developer trying to read a web map, one of the most important pieces of information you'll pull from the item information is the map extent. You then need to look in the web map data JSON and retrieve the spatial reference of the basemap. Using these two pieces of information, you can appropriately display the web map.