There are three more map scenes in the film, each of them as indifferent to the actual geography of that part of California, because Anderson isn't interested in the details of the layout, of course, but also because these would be real maps on which the fictional 'Little Boston, Isabella County' couldn't appear.
The next map scene is Plainview's visit to a real estate office, a two-shot sequence in which there are three maps on the wall, differentiated in look but hardly readable in detail. A fourth map is brought out after Plainview asks Al Rose the pertinent question: 'Well, where's the map?'
A short dvd-bonus on the research that went into the film shows two maps consulted, and a period photograph of maps being used: