Thanks for your note, History 101. I agree with you that some history books may seem light on research. This may not necessarily be a reflection on the author as much as a dearth of information on a topic. There is also the possibility of conflicting accounts and the question of which one to use. Selecting "incorrectly" could impact perceptions.
To your question about my book-- "how long did it take me to write the Maps of Antietam," I'd have to say about 30 years. The actual intense research, writing, and cartography, probably took about two years. One thing that I always do is to have knowledgeable historians review my books before they go to the publisher for editing. For the Antietam book, Tom Clemens and John Hopkak, both authors of important Antietam works, reviewed the book, as did Ted Savas, who does it while editing. If there is a loose thread or a vague thought, Ted will find it!
Hope you enjoy the book.