Sketching on Location by Matthew Brehm (blog | Flickr) is like a textbook on sketching, and it reads like one. The introduction even has a history on sketching from the days when people were drawing on parchment before paper was invented, to the present day where sketches are shared online.
There are lots of useful tips and techniques on sketching written in a conversational tone. Many of these tips can actually be found in other drawing books but this book focuses on drawing on location, hence all the examples are location drawings.
Using the sketch examples that Brehm drew himself, he talks about techniques like sighting and measuring, choosing subjects, setup and composition, perspective, applying value, using colours and including miscellaneous backgrounds for context. The book covers just enough of the basic sketching fundamentals and the instructions are explained very clearly. And there's insightful commentary as Brehm talks about the sketches he made.
This book is actually quite similar in scope with another book called Freehand Drawing and Discovery: Urban Sketching and Concept Drawing for Designers by James Richards. This book provides slightly more info on technical drawing skills though. The authors present the topics differently though from their perspective.
If you're a beginner starting out, I would also recommend Keys to Drawing. That's more hands-on to complement Brehm's book.
It's a good book overall but I felt that selling it at 57 dollars is quite pricy. It's a 176-page paperback and the paper feels like textbook quality paper -- soft.
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