The level of the layer's tileset model which is currently being displayed on the map. If the value is smaller than 0, the map is zoomed out beyond the first (lowest) level of the layer's model. If the value is larger than the last (highest resolution) level, then the map is zoomed beyond the highest available resolution of the model. If the value is exactly an integer, than this means the map scale corresponds to that level of the model. If the value is in between two integers, then the map scale is "in between" those two levels of the model.
Calculate the level of the layer's model that corresponds to the current map scale.
Note that when the return value is not an integer between the minimum and maximum level range of the layer's model, it is undefined what level will actually be used for visualization. The framework will make a best effort to select the most appropriate level.