Mapping and surveying services perform all of the activities that involve the physical measurement of land areas, including field surveying and data collection operations as well as the creation of maps using existing or acquired data. Mapping and surveying services are staffed by professional engineers and licensed land surveyors who use tools and equipment such as global positioning (GPS) base stations and portable GPS radio high-frequency (HF) receivers. Mapping and surveying services also use devices such as inclinometers, theodolites, and gyrotheodolites. With total-station theodolites, self-registering tachometers perform all of the necessary operations. Data is saved to an internal register or to an external storage device such as an electronic data collector. Mapping services that use other types of surveying instruments are also available.