The following will triangulate on a map the exact locations of his four attacks, encompassing his two phone calls and confirmed Zodiac letters, all of which fall within an approximate one half of a circle, drawn around his furthest two crimes, in what's known as the Canter and Larkin 'circle theory of environmental range'. In other words the greatest distance our killer seemed prepared to go.
What is noticeable, is that all these locations drop within a 180 degree segment of the circle, the center of the circle literally sits over the first two crime scenes and removing the Pleasanton mailing, the focus narrows right in to literally a third of a circle, giving us a very narrow field of view of the Zodiac's entire known activity. The 'hot zone' on this map sits over the Vallejo, American Canyon region, indicating the Zodiac Killer likely lived in this region and had a environmental range inside of 50 miles. If the Zodiac Killer lived in Vallejo and worked in San Francisco, then ideally mailing his letters away from his home residence makes logical sense. The San Rafael and Alamada County, Oakland areas are on a near direct traveling route, either side of the Bay Area, to and from San Francisco, if indeed the Zodiac Killer lived in Vallejo.
The killer made two phone calls, he may have had familiarity with the location of the Springs and Tuolumne intersection payphone, as it was an area he likely passed after his first two attacks, heading towards Columbus Parkway on both occasions and along Springs Road to the heart of Vallejo. In the second instance, a line drawn from Lake Berryessa to 1231 Main Street continues directly on to our center of focus, downtown Vallejo or the American Canyon region. These areas appeared to be the Zodiac Killer's comfort zone, but the prime focus always tends to a narrow region within 7 miles traveling distance from the first murders at Lake Herman Road on December 20th 1968, a remote, little used, two lane stretch of road, he appeared to know only too well.