The level, in combination with the tile width, tile height, and bounds of the named map, determines the zoom level of the tiles to be returned. The level shows how close the map image is to the Earth. Level 1 is the furthest away and is composed of one tile that the entire map will be drawn into. Level 2 is composed of 4 tiles, 2 across and 2 down. Each tile is a quarter of the entire map. Level 3 is composed of 16 tiles, 4 across and 4 down, and so on. The higher the level specified, the closer to the Earth the map image appears. For example, levels 1 to 3 usually show global or hemispheric detail, levels 4 to 15 show county/state/province level of detail and some larger cities, levels greater that 15 show street level views.
What the levels actually display is dependent on the named map hosted by the Map Tiling Service and the parameters in the named tile definition. For example, a level of 1 for a world map would be zoomed out to show the entire world. However, if you have a named map of a city or region where the bounds is less than the whole world, Level 1 would be zoomed in to show the regional or street level map.