A Glossary of Terms


Precision Farming


Aerial photography - Photos taken from airplanes to assist growers to determine variations within an area of interest such as a field.

ag consultant - Person trained in agricultural and management sciences to provide information to land owners/managers for a fee related to the farming operation.

ag consultant certification - There are 3 types of certification for ag consultants that are recognized in the US:

1. Certified Crop Advisor (CCA). Administered by the American Society of Agronomy.  Requirements include a high school education, 4 years of experience, continuing education credits and testing.

2. Certified Professional Agronomist (CPAg).  Administered by the American Society of Agronomy.  Requirements include a college education, 4 years of experience, continuing education credits and testing.

3. Certified Professional Crop Consultant (CPCC).  Administered by the National Alliance of Independent Crop Consultants.  Requirements include a college ag degree, 4 years of experience, continuing education credits and testing.

algorithm - A finite, ordered set of well-defined rules written as a computer program to assist in solving a specific problem.

agriculture anomaly - an agronomic (vegetation or soil) deviation or inconsistency in excess of "normal" variation from what one would expect to observe.

application - A practical use of computer software, an electronic system or a concept.

applications package - Specialized computer programs and their associated documentation developed for practical usage.  Ideally, applications packages allow a non-computer specialist to use the computer without learning complex programming languages. 

arc - A line described by an ordered sequence of points associated with vector data models.  When a node joins two or more arcs and several arcs are linked together in a loop, they form an area or polygon.

archive - The storage of historical records and data.  When you have collected a year or two of data from your precision farming applications, you have started your own archive.

ASCII - (American Standard Code for Information Interchange).  A standard coding system used to represent alphanumeric characters within a computer.  ASCII files enable the transfer of some data between different computers through the use of a common set of symbols.

aspect - Horizontal direction in which a slope faces (e.g., a SE facing slope has an aspect of 135 degrees).

attribute - A numeric and/or text description of a spatial entity (e.g., address or owner's name for a parcel).

attribute value - A value or property that is a characteristic of a spatial element.  For example, a specific symbol or color may represent 150-160 bushels/acre that is a value assigned to that attribute.

base map - The outline of your field with its proper coordinates is your base map.  Data collected within the field by your yield monitor will be defined in location by the base map, which is a binary digital map.

baud rate - A measure that describes the speed of the transmission of single digital elements over a communications line.  The number indicates how rapidly data could move through your modem or between a computer and a printer.


1. Used to define how comparisons are to be made between different computer software or systems according to specific requirements.

2. In surveying, a benchmark is the elevation at a specific point.

bit - An abbreviated term for binary digit, the smallest unit of computer data.

block kriging - A piecewise form of kriging based on grid cells.

buffer - An area defined by the specified length extended around a point, line, or area. 

byte - A unit of computer storage of binary data usually comprising eight bits, and equivalent to a character.  You will commonly hear computer memory and storage referred to using terms such as Kilobyte (approximately one thousand bytes), Megabyte (approximately one million bytes) and Gigabyte (approximately one billion  bytes).

cartography - The art and science of the organization and communication of geographically related information such as a yield image into maps or charts.  The term will refer to their construction, from data acquisition to presentation and use.

centroid - The position at the center of a one- or two-dimensional (2D) entity such as a polygon. 

choropleth map - A thematic map such as a yield image where quantitative spatial data is depicted through the use of shading or color variations of yield ranges.

computer aided design (CAD) - Software with the capability of performing standard engineering drawings.

computer aided mapping (CAM) - Software with the capability of generating standard mapping functions.  In contrast to GIS, it can not analyze or process a database.

contour - A line connecting a set of points, all of which have the same value.  A contour line will show elevations of the same value.

controller – An electronic device used to change product application rates on-the-g0, based on user directions or prescription applications maps.

crop scouting - Precise assessments of pest pressure and crop performance that can be tied to a specific location for better interpretation.

cross tabulation - Comparison by location of attribute data in two or more map layers.

customization - A procedure which produces an application or company specific interface and/or database design such as  yield mapping software.  For example, a customized version of a commercial yield monitor product may include menus that allow one to add individual field numbers and other identifiers into the database.

database - A logical collection of files managed as unit.  A GIS database includes data about both the position and the attributes of geographic features.

database management system (DBMS)  - A collection of software for organizing the information in a database that might contain routines for data input, verification, storage, retrieval, and combination.

data input - The entry of information into a computer through the use of a keyboard, digitizer, scanner, or even entering data from already existing databases.

data standardization - The process of achieving agreement on common data definitions, representation, and structures to which all data layers must conform.

DEM (Digital Elevation Model) - A digital representation of the elevation of locations on the land surface.  A DEM is often used in reference to a set of elevation values representing the elevations at points in a rectangular grid on the Earth's surface.  Some definitions expand DEM to include any digital representation of the land surface, including TIMS or digital contours.

differential correction - correction of the GPS signal to make it more accurate.  An uncorrected signal will be accurate to about 50 yards.  A corrected signal can be accurate to within 1-5 feet.  Correction of a signal is done from a second GPS receiver/transmitter at a known fixed location.  The signal is then transmitted to the tractor, combine or other equipment that corrects the proper location through differential processing.  There are four common ways to transmit a correction signal from the base station to the farm implement:

1. A dedicated AM transmitter that is located on a U.S Coast Guard tower located near coastal and inland waterways, which has a range of 100-250 miles.

2. A separate, private corporation satellite to send the corrected signal (OmniSTAR, RACAL), which has worldwide coverage.

3. Piggyback the correction signal on a commercial FM radio station frequency (DCI, ACCQPOINT), that has a range of 30-40 miles.

4. WAAS (Wide Angle Augmentation System) developed for the Federal Aviation Administration (FAA) which has US coverage.

digitizer - A table or tablet which has the capability of digitally recording the relative position of a cursor which is moved over the area or line that you want to digitize or record.

DLG (Digital Line Graph) - A US Geological Survey digital map format used to distribute topographical maps in vector form.  The digital files contain lists of the coordinate points that describe linear map features.

edit - The process of adding, deleting, and changing data/information on a computer.

expert system - A system designed for solving problems in a particular application area. One can draw an inference from a stored knowledge base that was developed by recording and structuring human expertise through an individual commonly called a knowledge engineer.

extrapolation - A method or technique to extend data or inferences from a known location to another location for which the values are not known.

feature - A geographic component of the earth's surface that has both spatial and attribute data associated with it (e.g., field, well, waterway).

field -

1. A set of alphanumeric characters comprising a unit of information.

2. A location in a data record in which a unit of information is stored.  For example, in your database, one of your crops may contain columns of data such as location #, crop type, variety, date of planting, etc. (all of which are fields)

3. A specific location on a person's farm that may  be called "Field # 10A"

field prescriptions – Applications of inputs at variable rates based on data obtained through yield monitors, crop scouting, remote sensing and soil sampling.

geocode - A code associated with a spatial element which describes its location.  An example would be a coordinate such as longitude or latitude.

geographic information systems (GIS) - System of computer hardware, software, and procedures designed to support the compiling, storing, retrieving, analyzing and displaying of spatially referenced data for addressing planning and management problems.

georeference system - A coordinate system keeping track of specific points on the Earth's surface.  Examples of such a system are the Universal Transverse Mercator system (UTM) and the State Plane Coordinate System.

geostationary satellites – Space vehicles in an orbit that keeps them over the same location on the Earth at all times.  Satellite-based differential correction signals are broadcast from this type of satellites.  Others are maintained by NOAA to provide weather images every 30 minutes of the Earth.

grid - A data structure that uses rectangular units or grid cells arranged in rows and columns to represent an area like a field.

grid mapping - Predetermined locations in a field where soil or plant samples may be obtained for analysis.  The test information can be used for assessing fertility needs and determining approximate locations for varying fertilizer and lime applications.

GPS (Global Positioning System) - A network of satellites controlled by the Defense Department that is designed to help ground based units determine their current location in latitude and longitude coordinates.  Note that the term "GPS" is frequently used incorrectly to identify Precision Farming.  GPS is only one technology that is used in Precision Farming to assist you to return to an exact location to measure fertility, pests and yield.

ground control point - An easily identifiable feature with a known location that is used to give a geographic reference to a point on a yield image. 

ground reference data - The field collection of data that is used in the interpretation of information gathered from other sources such as a yield image or a remotely sensed image.  Also known as ground truth but the preferred terminology is ground reference.

guided crop scouting – Assessment and recording of crop anomaly and conditions on a site-specific basis using a backpack GPS receiver and hand-held computer.  The system allows the user to record growth stage/maturity, plant vigor, presence of disease, weed and insect infestation.

hard disk - A large capacity, mechanical, magnetic, computer storage device that stores your programs and data. 

hardware - The various physical components of an information processing system such as a computer, view screen, plotters, and printers.

image classification - Processing techniques which apply quantitative methods to the values in a digital yield or remotely sensed scene to group pixels with similar digital number values into feature classes or categories.

input - An overused term that applies to the process of entering data into a computer.  Also used to describe the actual data that are to be entered. 

internet - An international network comprised of many possible dispersed local and regional computer networks in which one can share information and resources.  Developed originally for military and then academic use, it is now accessible through commercial on-line services to the general public.

kriging (creeging) - An interpolation technique for obtaining statistically unbiased estimates of spatial variation of known points such as surface elevations or yield measurements utilizing a set of control points.

layer - A logical separation of mapped information representing common data (e.g., roads, soils, yields, vegetative cover, and soil tests).

lat/lon - Refers to Latitude and Longitude that specifically describes a position on the earth.  Latitude is the north to south position.  Longitude is the east to west position.  Precise locations are described in degree, minutes and seconds.  The lat/lon of Purdue University is 86 degrees, 55 minutes, 05 seconds latitude and 40 degrees, 25 minutes, 50 seconds longitude.

legend - A map section containing explanations of symbols, colors and/or shades that signify various elements and data values on the map.  A yield map will contain a listing of yield values and the color denoting a range of yields.

LIS (Land Information System) - A system for describing data about land and its use, ownership and development.  LIS refers to all aspects of handling the data such as collection, storing, checking, merging, manipulating, analyzing and displaying.

locational reference - Referencing data collected by yield monitor, sensor or other method and relating it to a specific spatial position.

lookup table - A reference table containing key attribute values that can be linked or related to data usually collected at a specific location.  An example would be physical and chemical data relating to a soil-mapping unit.

menu - A list of options displayed by a computer data processing program, from which the user can select an action to be initiated.  These choices are usually displayed in the form of alphanumeric text but may be as icons.

merge - To take two or more maps or data sets and combine them together into a single coherent map or database without redundant information.

metadata - A term used to describe information about data.  Metadata usually includes information on data quality, currency, lineage, ownership, and feature classification.

mosaic - Process of assembling GIS database files for adjacent areas into a single file.

network -

1. A group of linked computers that are able to share software, data, and various hardware devices such as printers. 

2. A geometric or logical arrangement of nodes and interconnecting lines.

noise - Random variations or error in a data set.  Also an unwanted sound coming from the combine.

output - The product of a computer process and analysis that may be displayed on a computer screen, or as a printed map or tables of values.

orthophotograph - An aerial photograph that corrects distortion caused by tilt, curvature and ground relief.

pixel - A term used in remote sensing referring to the fundamental unit of data collection which is an abbreviation for "picture element".  A pixel is represented in a remotely sensed image as a rectangular cell in an array of data values and contains a data value that represents a measurement of some real-world feature.

point sampling - A method of grid sampling in which a sample is taken in a 10-30 foot radius at the center point of each grid location.

polygon - An area enclosed by a line describing spatial elements, such as a similar yields range, land use or soil type.

precision farming - Using the best available technologies to tailor soil and crop management to fit the specific conditions found within an agricultural field or tract.

raster-to-vector conversion- A process in which one converts an image such as a yield map of grid cells into a data set layer of lines and polygons.

RDBMS (Relational Database Management System)  - A database management software system that organizes data into a series of records that are stored in linked tables.  This provides the ability to relate different records, fields and tables, and aids data access and data transformation.

registration - A process where one can geometrically align maps or images to allow one to have corresponding cells or features.  This allows one to relate information from one image to another, or a map to an image, such as registering a yield image to a soil map to determine if soils are influencing the yield response.

remote sensing - The act of detection and/or identification of an object, series of objects, or landscape without having the sensor in direct contact with the object.  The most common forms include color and color infrared aerial photography, satellite imaging and radar sensing.

resolution - A way of detecting variation.  In remote sensing, one has spatial resolution (the variation caused by distance separating adjacent pixels), spectral resolution (the variation from the range of spectral responses covered by a wavelength band), and temporal resolution (the variation caused by time over the same location).

satellite constellation - A system of 24 satellites that is owned by the US Department of Defense (DOD) that can determine location to within inches.  There are usually at least 4 of these satellites that are in view 24 hours a day. The DOD can intentionally introduce error into the signal during national emergencies.  This error called “Selective Availability” would allow an accuracy of approximately 50 yards without differential correction.

scale - The ratio or fraction between the distance on a map, chart, or photograph and the corresponding distance on the ground.  A topographic map has a scale of 1:24,000 meaning that 1-inch on the map equals 24,000 inches (2,000 feet) on the ground.

site-specific management – Use of high-tech equipment to enable the farmer/producer to thoroughly assess field conditions and the applications of inputs to help obtain the best possible financial return.

software - The programs, procedures, algorithms (set of rules), and their associated documentation, for a computer system.

spatial data - Data pertaining to the location, shape, and relationship among geographical features.

thematic map - A map related to a topic, theme or subject.  These maps emphasize a single topic such as yield, soil type, or land ownership.

topologically integrated geographic encoding and referencing (TIGER) file - The nationwide digital database developed by the US Bureau of the Census.  TIGER files contain street addresses and census boundaries with accompanying population statistics.

turn-key system - A reference to hardware and/or software systems meaning that they are ready to be used immediately and are designed, provided at a cost and supported by a commercial group.

UTM (Universal Transverse Mercator)  -  A commonly used map projection that uses a set of transverse mercator projections for the globe which are divided into 60 zones, each covering 6 degrees longitude.  Each zone has an origin of the central meridian and latitude of 0 degrees.

Variable-rate technology - Instrumentation such as a variable-rate controller for varying the rates of application of fertilizer, pesticides and seed as one travels across a field.

waveband - A remote sensing term used to describe a contiguous range of wavelengths of electromagnetic energy.  Visible wavelengths (seen by the human eye) which range from 400 to 700 nanometers.  Near infrared (NIR) wavelengths are at 700 to 2600 nanometers.

yield maps – A representation of crop yields collected on-the-go by a harvester equipped with an instantaneous yield monitor. Each location/site (pixel) in a field is assigned a specific crop yield value.

yield monitoring - Regular intervals where a harvested weight has been obtained along with a GPS reading.  A display of the weights every 1-3 seconds is translated to bushels/acre or yield providing a yield map.  Moisture of the grain is obtained at the same time.

zoom - To enlarge or decrease the scale of an image that is being displayed.  One can “zoom out” of a yield monitor image and enlarge it in a progressive scaling of the entire image or one can “zoom in” decreasing the scale.

z-value - A commonly used reference referring to elevation values.  The “z direction” refers to upward direction on a 3-D chart or diagram.




Compiled by Chris J. Johannsen, Professor of Agronomy, Purdue University, johan@purdue.edu


Revised November, 2000


Acknowledgment:  A special thanks to all the friends and colleagues who provided additions, comments and corrections to this Glossary, originally published in October, 1995. 

Partial funding for this effort received from Stennis Space Center, (NASA Grant NAG13-00001S).