Geologist James Skinner of the USGS (U.S. Geological Survey) oversees the production of standardized maps for solar system bodies. Skinner and colleagues used information from six regional lunar maps created by separate research groups during the Apollo era, and combined them with recent lunar orbiter observations to draw up a new comprehensive geologic map of the whole moon, including views of the north and south lunar poles.
However, it was not just a matter of overlaying the six Apollo-era maps one on top of another and adding recent lunar orbiter observations to bring the data up-to-date. The pictures did not all line up exactly. Also, since separate research groups worked on the maps at different times using knowledge they had at that time, they interpreted what they saw differently. At times, two different teams looking at the same surface features would label them differently. Skinner and colleagues availed themselves of recent lunar orbiter observations to painstakingly reconcile the discrepancies and come up with the final spectacular result.
Different colors on a new geologic map of the moon designate different types of rock and sediment formations on the moon. For instance, craters associated with the Eratosthenian period on the moon (about 3.2 billion to 1.1 billion years ago) are typically marked green. Craters from the older Imbrian period (around 3.9 billion to 3.2 billion years ago) are generally painted blue.