I agree that some of the findings and comments of Greaves and Berriman, and also some of the early metrology findings and comments by Petrie, are relevant to my article, so I added a few pages at the end.
Sea level is the standard for the radius and circumference. A 100 foot change in sea level would be 200 feet of diameter and approximately 1/10 of a mile of circumference. Based on approximately 25,000 miles in the circumference, the effect on each mile would be 1/(25000 x 10). For a foot it would be 1/(25000 x 10 x 5280). For an inch it would be 1/(25000 x 10 x 5280 x 12). For a one foot change in sea level you can add two more decimal places. The different elevations of mountains and valleys has zero effect on the coordinates of any location.