I've added two new chapters to the Our Galactic Region book. These are a description of the basic plan of the Milky Way and an explanation of several techniques that astronomers use to estimate distances, Surveying the Galaxy.
I never had a basic plan description for the Milky Way before on this site because I assumed that this kind of information is widely available elsewhere. But a look around the Web showed that this was not really true and much of the information that was available was incorrect or outdated. (It doesn't help that astronomers cannot even agree on the names of the spiral arms and so many people get the impression that there are more spiral arms than there really are.)
I've also added an improved introduction to the Face-on map overview chapter.