Cartographers in the Field
This Depression-era oil painting was created by USGS field man Hal Shelton in 1940. The painting depicts mapping techniques used in the early days of cartography, including an alidade and stadia rod for determining distances and elevations and a plane-table for sketching contour lines. A USGS benchm...
Location: Menlo Park, CA, USA

High Standard Alidade
This alidade consists of straightedges with a rigidly-mounted telescope that can be rotated through the vertical angle ±30. The telescope is set on a high standard or post (4 inches in height) to raise it above the table. The telescope for the high standard is 16 power, inverting type with internal ...
Location: USA

Gurley Micrometer Alidade
Manufactured by W. & L.E. Gurley, Troy, New York. The micrometer attachment us a modification of the tangent screw attached to the horizontal axis of the telescope and used for measuring vertical angles in terms of their tangents. Relatively few of these types of alidades are listed in early 1900s p...
Location: USA

Pendulum Self-leveling Alidade
This is a telescopic alidade in which a pendulum device, or compensator replaces the conventional bubble for establishing a horizontal reference line from which vertical angles may be measured. Alidades were the primary mapping instrument in the U.S. from about 1865 to the 1980s, when they were repl...
Location: USA

Explorer’s Alidade
Manufactured by Keuffel & Esser, New York & New Jersey. In this type of alidade, as opposed to the high standard, the telescope mounted close to the straightedge, producing a more compact instrument. A right-angle prism is attached to the eyepiece and permits viewing by looking down. A cylindrical b...
Location: USA

Telescopic Alidade
A high standard alidade; this type of alidade permits direct viewing through the telescope. The level is mounted below the inverting telescope and the base (blade) is solid brass with circular voids. Manufactured by Keuffel & Esser, New York & New Jersey. Object ID: USGS-000165...
Location: USA

Expedition Alidade with Case
The rectangular base (blade) features two different types of spirit levels and a trough compass. Manufactured by W. & L.E. Gurley, Troy, New York. Object ID: USGS-000328...
Location: USA

Open-sight Alidades
Open-sight Alidades. This type of alidade is a straightedge with a sighting device parallel to the edge. Early alidades were simple bars with open sights on either end, while telescopic alidades were introduced in the early 1800s. The examples here of solid brass and an early plastic/wood combinat...
Location: Reston, VA, USA