A bearing in surveying is a way of expressing the direction of a line between two points on the ground. It describes the horizontal angle that a survey line makes relative to a north-south reference line, broken into one of four quadrants: northeast, southeast, southwest, or northwest. Bearings are fundamental to nearly every type of survey work, from marking property boundaries to aligning roads and pipelines.
How Bearings Are Written
A bearing always starts with either N (north) or S (south), followed by an angle, and ends with either E (east) or W (west). The angle sits between 0 and 90 degrees because it only measures the rotation within a single quadrant. For example, N45°E means a line angled 45 degrees east of due north, while S30°15’W means a line angled 30 degrees and 15 minutes west of due south.
This three-part format (reference direction, angle, turning direction) makes bearings intuitive to read. When you see S72°E, you can picture starting at south and rotating 72 degrees toward east. The angle never exceeds 90 degrees, so there’s no ambiguity about which quarter of the compass you’re in.
For higher precision, angles are broken into degrees, minutes, and seconds. One degree contains 60 minutes, and one minute contains 60 seconds. A bearing like N43°00’36″E is common in legal property descriptions and professional survey plats.
Bearings vs. Azimuths
Azimuths and bearings both describe direction, but they use different scales. An azimuth is measured as a single clockwise angle from north, ranging from 0 to 360 degrees. A bearing splits that same circle into four quadrants and keeps the angle at 90 degrees or less. The two systems are interchangeable, just expressed differently.
An azimuth of 141°25’34” falls in the southeast quadrant. To convert it to a bearing, you subtract it from 180°, giving S38°34’26″E. An azimuth of 230°12’20” is in the southwest quadrant, so you subtract 180° from it to get S50°12’20″W. An azimuth of 330°35’48” is in the northwest quadrant, so you subtract it from 360° to get N29°24’12″W. And any azimuth under 90° translates directly: an azimuth of 43°00’36” becomes N43°00’36″E.
The conversion rules break down by quadrant:
- Northeast (0° to 90°): The bearing angle equals the azimuth. Prefix with N, suffix with E.
- Southeast (90° to 180°): Subtract the azimuth from 180°. Prefix with S, suffix with E.
- Southwest (180° to 270°): Subtract 180° from the azimuth. Prefix with S, suffix with W.
- Northwest (270° to 360°): Subtract the azimuth from 360°. Prefix with N, suffix with W.
Azimuths are more common in military and navigation contexts because they give a single number. Bearings are preferred in land surveying and property descriptions because the quadrant notation maps neatly onto how boundaries are drawn on a plat map.
Forward and Back Bearings
Every survey line has two directions. If you’re standing at point A looking toward point B, that’s the forward bearing. If you’re standing at point B looking back at point A, that’s the back bearing. In plane surveying, the back bearing has the same angle as the forward bearing but the opposite letters. A forward bearing of N45°E becomes a back bearing of S45°W.
This relationship is useful for checking field measurements. If a surveyor measures the bearing in both directions and the results don’t match (after flipping the letters), it signals an error in the measurement or a local disturbance affecting the compass.
Which “North” the Bearing Uses
Not all bearings reference the same north. There are three versions, and knowing which one a survey uses matters.
True north is the direction toward the geographic North Pole. It’s the most stable reference because it doesn’t change over time. Surveyors can determine true north by observing the position of Polaris (the North Star) or by using GPS-based positioning systems.
Magnetic north is where a compass needle points. It doesn’t align perfectly with true north because the Earth’s magnetic poles wander. The difference between magnetic north and true north at any given location is called magnetic declination. In some parts of the United States, declination can be over 15 degrees, which would throw a property boundary off by a significant distance if left uncorrected.
Grid north is the north direction on a coordinate system used for mapping, such as a state plane coordinate grid. It’s based on the map projection and may differ slightly from true north depending on your position within the grid zone.
Washington state survey standards, which are representative of requirements nationwide, mandate that every survey plat clearly state the basis for its bearings: whether the surveyor used a Polaris observation, a GPS-derived azimuth mark, a compass with a stated declination, or an assumed reference direction. If the bearing basis differs from what’s recorded in the property’s existing title, that difference must be noted.
Correcting for Magnetic Declination
If a bearing was measured with a compass, it references magnetic north and needs a declination correction to convert to true north. The correction is straightforward: you add or subtract the local declination value depending on whether the declination is east or west. NOAA’s National Centers for Environmental Information maintains an online calculator that provides the current declination for any location.
This correction is especially important when retracing old surveys. A property boundary surveyed with a compass in 1920 used the magnetic declination of that era, which could differ by several degrees from today’s value. Surveyors account for this shift when interpreting historical records.
How Bearings Are Measured in the Field
Modern surveyors rarely use a magnetic compass for precise bearing work. The standard instrument is a total station, an electronic device mounted on a tripod that measures both horizontal angles and distances with high precision. Robotic total stations use motorized tracking to follow a target prism, allowing a single surveyor to collect angle and distance data without an assistant.
Theodolites, the predecessors to total stations, measure horizontal and vertical angles but not distances. They’re still used in some contexts, though total stations have largely replaced them because they combine angle measurement with electronic distance measurement in one device. GPS and GNSS receivers also provide bearings by calculating coordinates for two points and deriving the direction between them.
Regardless of the tool, the surveyor establishes a known reference direction first, then measures the angle from that reference to each survey line. The raw angle is then expressed as a bearing or azimuth for recording on the plat.
Accuracy Requirements
Bearings on a professional survey aren’t just approximate directions. They must meet specific accuracy standards set by state regulations. Washington state’s minimum standards offer a useful example. For boundary surveys, positions must be accurate to within 0.07 feet plus 200 parts per million at a 95% confidence level. That means for every 1,000 feet of measured distance, the allowable positional error is roughly 0.27 feet (about 3.2 inches).
Angular closure requirements (how well the measured angles add up when you return to your starting point) also vary by land use. In central business and industrial areas, field traverses must close to at least 1:10,000, with a maximum angular error of 10√n seconds, where n is the number of angles measured. In residential, suburban, and rural areas, the standard is 1:5,000 with a maximum angular error of 30√n seconds. A 10-angle traverse in a residential area, for instance, could tolerate up to about 95 seconds (roughly 1.6 minutes) of total angular error.
Where Bearings Show Up in Practice
Bearings appear in almost every document that describes land. Your property deed likely contains a legal description built from a series of bearings and distances: “thence N43°00’36″E a distance of 150.00 feet” tells anyone exactly which direction and how far that boundary line runs. Strung together, these calls trace the entire perimeter of a parcel.
Beyond property boundaries, surveyors use bearings to lay out road alignments, position utility corridors for water and sewer lines, and establish control networks for construction projects. Route surveys for canals, pipelines, and highways depend on bearings to keep the alignment on course over long distances. When a building needs to be staked out on a construction site, the corners are positioned using bearings and distances from known reference points.