Glossary of Terms

A-B Line

A reference line set for each field that a guidance system of a tractor or other vehicle follows.


(GPS) The measure of closeness of an object's actual (true) position to the position obtained with a GPS receiver. Accuracy levels are used to rate the quality of GPS receivers.

Active Sensor

A device that generates a signal, bounces it off an object, and measures the signal reflected from the object.


A mathematical formula that may be used to control variable rate applications.


A deviation or inconsistency in excess of the normal variation from what one would expect to observe.

Application Map

A plan showing the location and rate at which inputs such as seeds, fertilizers, or pesticides will be applied across a field, derived manually or automatically from analysis of yield maps or according to field grids or zones.

Artificial intelligence (AI)

The mechanism by which a machine can take input from the environment via sensors, process this input using the experiences it has gained and take rational and intelligent decision on the environment using actuators, much like how humans do.

As-applied map

Contains information about the location and rate of application for inputs such as seeds, fertilizers, or pesticides. Usually created with a GPS equipped applicator and data logger.

ASCII (American Standard Code for Information Interchange)

Widely used computer code for identifying numbers, letters and special characters.


Direction in which a slope faces.

Assisted steering

An adaptation of the steering system of an existing vehicle to GPS automation by replacing the standard steering wheel with a powered version, or fitting a drive mechanism to it. An example is Trimble’s E-Z Steer.

Auto-Steer, AutoPilot, Autoguidance

A system that steers agricultural equipment. It includes both the GPS system to receive and process the signals, software and hardware to allow the input of control maps and the mechanical equipment to actually steer the tractor.

Autonomous operation

Vehicle guidance without the need for human intervention. A tractor may be driven by a series of on-board sensors and GPS.

Base station

Also called a reference station, is a receiver located at a surveyed benchmark. The base station calculates the error for each satellite and through differential correction, improves the accuracy of GPS positions collected at unknown locations by a roving GPS receiver.

Bayes’ Theorem

Gives the probability of an event when we already have information about some other condition related to the event.