This tool makes it easy to label various lunar feature groups on your screen display, as well as on your printed maps. When you open the Labeler, the dialog box (shown below), appears on your screen. Simply use your mouse to place check marks next to the feature names that you want displayed on the map, and click, Apply.
Unchecking a box and clicking, Apply again removes the labels. Labels can be useful when exploring the moon on your computer monitor, and are a necessity when you are printing maps for use at the telescope eyepiece.
The Labeler also gives you have the ability to proportionally adjust all font sizes simultaneously. This allows you to quickly set an appropriate label scale, as you zoom the map in and out. Simply adjust the slider, by moving it towards smallest or largest, and click, Apply.
In order to help reduce map overcrowding, all features types, (with the exception of crater names), are identified by a two-letter prefix, derived by the IAU (International Astronomical Union) and used by the USGS (United States Geological Survey). The designations used are as follows:
NOTE: Checking all of the feature groups at once will overload the map with data and will also increase the map redraw time, so be careful not to over annotate.
You will notice that Lettered Sub-Craters and Lunar Domes are not included within the group labeling categories. Since the Lettered sub-craters number in the thousands, the map would be completely overwhelmed by the label density. In the case of domes, they tend to cluster in groups that are extremely close to one another, so label overlapping will often make dome labels unreadable.
Both groups of features can be easily identified by using the Hover, or they can be labeled by using the custom labeling capability found in the Feature Finder.