Minecraft wiki entry for Map_item_format, associated text: The root tag.
 data: The map data.
 scale: How zoomed in the map is (it is in 2scale wide blocks square per pixel, even for 0, where the map is 1:1). Default 3, minimum 0 and maximum 4.
 dimension: For <1.16 (byte): 0 = The Overworld, -1 = The Nether, 1 = The End, any other value = a static image with no player pin. In >=1.16 this is the namespaced ID of a dimension instead. [more information needed]
 trackingPosition: 1 (default) indicates that a positional arrow should be shown when the map is near its center coords. 0 indicates that the position arrow should never be shown.
 unlimitedTracking: 1 allows the player position indicator to show as a smaller dot on the map's edge when the player is farther than 320 * (scale+1) blocks from the map's center. 0 makes the dot instead disappear when the player is farther than this distance. Defaults to 0 for maps created from an empty map and 1 for Explorer Maps.
 locked: 1 if the map has been locked in a cartography table.
 xCenter: Center of map according to real world by X.
 zCenter: Center of map according to real world by Z.
 banners: List of banner markers added to this map. May be empty.
A banner marker.
 Color: The color of the banner. Allowed values: white, orange, magenta, light_blue, yellow, lime, pink, gray, light_gray, cyan, purple, blue, brown, green, red, black.
 Name: The custom name of the banner, in JSON text. May not exist.
 Pos: The block position of the banner in the world.
 X: The x-position of the banner.
 Y: The y-position of the banner.
 Z: The z-position of the banner.
 frames: List map markers added to this map. May be empty.
A marker.
 EntityId: Arbitrary unique value for the marker.
 Rotation: The rotation of the marker, ranging from 0 to 360.
 Pos: The block position of the marker in the world.
 X: The x-position of the marker.
 Y: The y-position of the marker.
 Z: The z-position of the marker.
 colors: Width * Height array of color values (16384 entries for a default 128×128 map). Color can be accessed via the following method: colorID = Colors[widthOffset + heightOffset * width], where (widthOffset==0, heightOffset==0) is left upper point.
 DataVersion: The version the map was created. If not present, defaults to 1343 (1.12.2)