Stephen Van Hoven, chief of the Horticulture Division at Arlington National Cemetery, uses a detailed reference map and coordinate system to determine the precise position of a tree he is examining in the Millennium Project site at Arlington National Cemtery in Arlington County, Virginia, in the United States on February 6, 2013. The Millennium Project will clear 27 acres of property on the cemtery grounds, and add an additional 30,000 burial and inurnment sites. Horticultural experts estimated the age of all trees in the Millennium Project site based on height, trunk circumference, and other factors. Many of the oldest, non-invasive trees will be retained. Experts use the data collected from initial trees cut down as part of the project to confirm these estimates of age.