The city of Detroit is using desktop appraisals to determine property values. Desktop appraisals involve looking at aerial photos of properties and information gathered from parcel maps, deeds and permits, in stead of going to look at it in person. They are a quicker way of keeping up with about 71,000 residential parcels that need to be valued each year. Up until 2017, 60 years had passed without Detroit finishing a comprehensive reappraisal of city property values. After playing catch up, the assessor’s office must keep current with a state requirement that 20 percent of properties be reassessed each year. Aerial technology aids the city in keeping up with the huge number of homes over about 140 square miles. The strategy has critics who say that aerial imagery can cause low-value property owners to be in over their heads when their properties are already over-assessed. A shortage of appraisers has contributed to the reliance on desktop appraisals.