Global Positioning System (GPS) is a space-based navigation system that uses a constellation of satellites to determine the location of the receiving unit on Earth. GPS satellites circle the globe in a precise orbit, transmitting coded radio signals; at least four of their signals can reach any given point on Earth at one time. These signals can pass through clouds, glass, and plastic; the signals weaken when passing through solid objects such as buildings and cannot pass through objects that contain high levels of metals. For land conservation purposes, it is important to note that a GPS unit will not receive satellite signals when under thick forest canopies, underground, or underwater.
Although GPS was originally developed in the 1980s for military purposes, today the technology provides positioning, velocity, and navigation information for a wide range of users.
GPS helps conservation organizations and municipalities manage land by recording positional data in the form of points (e.g., location of a tree or property corner), lines (e.g., a trail), or areas (e.g., a lake). By importing the data into Geographical Information System (GIS) software, users can create maps of this data.
To use GPS effectively, an organization must invest in some combination of equipment and software, and either train or hire staff to operate it.
Mapping Landscape Features
GPS enables users to map the location of a wide variety of features in the field, such as mature forest, specimen trees, invasive species, soil erosion, fire-disturbed areas, riparian buffers, and waterways. Users can also map human-made features like trails, benches, buildings, roads, driveways, and fences. Once mapped, these features can be easily located with a GPS device on return visits to the property.
Linking Photos to GPS Coordinates
Users can take digital photos in the field and link them to GPS coordinates in the GIS database. This allows users to establish a visual record of important features and their precise locations. By comparing photos of the same location taken at different times, users can notice changes to the property. (This can be particularly helpful for monitoring easements and identifying potential violations.)
Documenting Property Boundries
GPS allows users to document the coordinates of property boundaries. In the past, surveyors used landmarks (which can be destroyed or moved over time) to define boundaries. Since GPS uses exact coordinates rather than relational landmarks, it produces measurements that remain accurate no matter what happens to the surrounding land or physical objects used as landmarks. (Note that accurate surveying of property boundaries necessitates the use of survey-grade equipment; see the heading “Survey-Grade” below. Also, depending on the purpose of the survey, the law may require the work to be completed by a licensed surveyor.)
Documenting Other Boundries
Land trusts can use GPS to document boundaries between areas subject to different levels of restrictions under a conservation easement, for example, the border between an area that is to remain in a largely wild state and an area where farming is permitted.
A GPS receiver is the electronic unit that receives satellite signals and produces positional data, which can then be analyzed using mapping software. GPS devices vary greatly in price and quality. Since technology is always improving, it is best to research current receivers before making a purchase. Some companies rent receivers, which gives organizations the chance to test different receivers before making an investment.
Types of GPS Recievers
These units are the least expensive. Designed for outdoor recreation activities like hiking and camping, they provide basic latitude and longitude coordinates while plotting points of interest and straight-line routes. Most are accurate within five to 10 meters. Users can only identify points with a short name and ID number; additional attributes must be recorded manually and entered into GIS software. Basic units generally cost between $200 and $500.
These units are more sophisticated. They allow for enhanced data collection, greater map detail, and more precise navigation. When enabled with WAAS (Wide Area Augmentation System), they are accurate within three meters; with the use of differential GPS, accuracy can be as close as one meter. Some can also receive additional signals from GLONASS satellites for even greater accuracy. Most come with base maps installed; more detailed maps are available for purchase. Units may have additional features like touch screens or built-in cameras. Garmin, Trimble, and Magellan are the leading companies offering map-grade units; Trimble offers the most advanced (and expensive) units. Units can cost from $500 to thousands of dollars depending on level of accuracy and other features.
Smartphones and tablets are another option. With built-in software or downloadable GPS applications like MotionX, GPSLogger, and GPX Viewer (recommended by multiple land trusts), they can perform some of the same functions as a commercial-grade handheld GPS. An internet search reveals a wide variety of GPS applications for both Apple and Android devices, and most of them only cost a few dollars.
Used by surveyors for precise measurements, these units are extremely accurate, sometimes to within a centimeter. They can cost tens of thousands of dollars and require extensive training and expertise, making them impractical for most land trusts and municipalities.
A recent development in GPS technology for land trusts is the use of unmanned aerial vehicles (UAVs, also known as drones) to collect data-enabled aerial imagery of properties. Since UAVs receive GPS signals, each video image they collect is linked to a specific location. Platforms like Survae allow land trusts to use this data in a variety of ways, from creating GIS map layers to monitoring easements over time. They also allow users to create customized routes, which UAVs can fly at specified elevations. Land trusts may hire licensed pilots to conduct the flights, eliminating the need to train staff or purchase UAVs themselves.
There are several factors to consider when purchasing a unit:
- Accuracy. Different receivers provide different levels of accuracy.
- GIS Data Integration. Some units convert GPS points to specific GIS or Google Earth formats, which may or may not be compatible with certain mapping software.
- Attributes. Many GIS users have found that accurate attribute collection is just as crucial as location acquisition. Only the more advanced map-grade GPS units allow users to collect and input detailed attribute information.
- Device Compatibility. Some GPS units can wirelessly synch with digital cameras, rangefinders, or other field devices to receive additional data; this might require additional hardware or software. Other models have built-in cameras.
- Memory Capacity. Units that use auxiliary memory cards in addition to internal storage allow users to purchase morel memory capacity in the future, if necessary. Some unit/software combinations allow users with an internet connection to upload data directly from the unit to the cloud for storage.
- Durability. Some units are designed for use in rugged environments, with features like water-resistant screens, push-button controls, and protective outer casing.
- Battery. Some units use standard batteries, while others use internal rechargeable batteries. A device that includes a sleep mode or battery-save function will extend battery life while in the field.
For general information about choosing a GPS receiver, see:
“Tips on Selecting the Right GPS Receiver, for Your Job” (Resource Analysis)
“Maps & Geospatial: Global Positioning System (GPS)” (Penn State)
For product comparisons and reviews, see:
“Best Handheld GPS Review” (Outdoor Gear Lab)
“Handheld GPS for Surveyors” (Land Surveyors United)
There are many GPS software packages available on the market. Many are free. These are some of the most prominent applications.
Installed on GPS Unit
ESRI software for GPS units that allows mobile field mapping and data collection. Purchase required; free trial available.
Trimble GPS Pathfinder
Office software that supports all aspects of GIS data collection and maintenance for most Trimble GPS receivers. Purchase required.
Previously known as MapSource, a free mapping software compatible with most Garmin GPS units.
Installed on Computer or Other Device
Free virtual globe, map, and geographic information program. Google Earth Pro is available for desktop; in early 2017, Google Earth for Chrome was released as a non-desktop version. Some GPS units have a direct download to Google Earth. See the user’s guide for more information.
Free application developed by the Minnesota Department of Natural Resources that allows users to transfer data between GPS receivers and GIS software. Users can upload or download waypoints, tracks, and routes; calculate shape attributes; hyperlink images; and more. It is compatible with most Garmin GPS units and NMEA-output units from other companies.
MapGuide Open Source
Free platform that enables users to create their own maps and mapping applications. Includes an XML database for storing and managing content, and supports most geospatial file formats, databases, and standards.
Free GPS mapping software with a variety of features that allow users to geotag photos, blend different map types, and visualize multiple routes simultaneously.
Organizations should create protocols for collecting data, focusing on consistency and accurate documentation. GPS users should always record the source of and expected precision of data, which allows it to be combined with other data and ensures that future users will know exactly how it was collected. If not documented appropriately, data might be unusable in the future.
The admissibility of GPS data in a court of law varies depending on who collected the data and how they collected it. A court will accept a property boundary determined by a licensed surveyor using a survey-grade GPS. It is less certain how a court might view geographic information recorded by land trust staff using a non-survey-grade GPS unit, for example, the boundary between areas that have different levels of protection in a case where a newly constructed building appears to encroach on an area in which it is not permitted.
For more information about legal risks and implications, organizations should discuss GPS practices with their legal counsel.
See “Stewardship Tools: Who’s Using What?”, published in LTA’s Saving Land magazine, to see comments from different land trusts about their preferred GPS units and applications (as of 2016).
See the website GPS Tracklog for GPS-related news, reviews, buyer’s guides, and more.
See the website GIS Lounge for information about GIS mapping software, GPS tutorials, and more.
The Global Positioning System (GPS) is a space-based radio-navigation system consisting of a constellation of satellites broadcasting navigation signals and a network of ground stations and satellite control stations used for monitoring and control.How accurate are GPS calculations? ›
The GPS unit is normally accurate to within two meters Circular Error Probability (CEP), and the accuracy is further increased through algorithms built into GPS Insight. Analysis of the GPS information provided by GPS Insight yields an accuracy rate of approximately 99.88%.How accurate are Global Positioning System GPS receivers on average? ›
GPS receivers are accurate to within 15 meters (49 feet) on average. Certain atmospheric factors and other sources of error can affect the accuracy. Accuracy can be improved with a Differential GPS (DGPS) or WAAS (Wide Area Augmentation System).How many global positioning systems are on GPS? ›
Users of Satellite Navigation are most familiar with the 31 Global Positioning System (GPS) satellites developed and operated by the United States. Three other constellations also provide similar services. Collectively, these constellations and their augmentations are called Global Navigation Satellite Systems (GNSS).What are the 3 types of GPS? ›
- A-GPS. Assisted GPS (A-GPS) is a type of GPS that allows receivers to get information from local network sources, which helps in the location of satellites. ...
- S-GPS. ...
- D-GPS. ...
- Non-differential GPS. ...
- Mapping and non-mapping GPS.
GPS is a system of 30+ navigation satellites circling Earth. We know where they are because they constantly send out signals. A GPS receiver in your phone listens for these signals. Once the receiver calculates its distance from four or more GPS satellites, it can figure out where you are.Can GPS be wrong? ›
Many things can degrade GPS positioning accuracy. Common causes include: Satellite signal blockage due to buildings, bridges, trees, etc. Indoor or underground use.What is the best GPS accuracy? ›
The United States government currently claims 4 meter RMS (7.8 meter 95% Confidence Interval) horizontal accuracy for civilian (SPS) GPS.Why is GPS accurate? ›
Conditions That Affect GPS Tracking Accuracy
GPS uses the frequency of radio signals to determine the location of a device. This means that the GPS device can make these calculations by measuring the time it takes for radio signals to be received from several satellites orbiting the earth.
An output wire on a gps device, allows a signal to be sent from the device to an endpoint. Think of it as you being able to “energize” the output wire – and its like the wire saying – “Hey! I am sending a Signal Here, I'm On”. Two types of signals that you can send when you engage an output wire are latched or pulsed.
The Global Positioning System is a constellation of orbiting satellites that provides navigation data to military and civilian users all over the world. The system is operated and controlled by the 50th Space Wing, located at Schriever Air Force Base, Colo.How strong is GPS signal? ›
The typical power level of the GPS signal is -125 dBm.Is GPS speed more accurate? ›
With a clear view of the sky, GPS speed has shown to be more accurate than most vehicle speedometers.How can I improve my GPS signal strength? ›
- Make Sure the Software on Your Phone is Up to Date. ...
- Use WiFi Calling When You're on a Reliable Internet Connection. ...
- Disable LTE If Your Phone is Showing a Single Bar. ...
- Upgrade to a Newer Phone. ...
- Ask Your Carrier About a MicroCell. ...
- Change to a Different Carrier.
GPS is an abbreviation that means gallons per second, or is short for global positioning system, which is a network of satellites which can be used to locate vehicles and people. An example of GPS is how a person can be tracked while driving from New York to California.What is the main function of GPS? ›
What is GPS? GPS is a positioning system based on a network of satellites that continuously transmit coded information. The information transmitted from the satellites can be interpreted by receivers to precisely identify locations on earth by measuring distances from the satellites.What are the application of GPS? ›
GPS technology is now in everything from cell phones and wristwatches to bulldozers, shipping containers, and ATM's. GPS boosts productivity across a wide swath of the economy, to include farming, construction, mining, surveying, package delivery, and logistical supply chain management.How does GPS calculate position? ›
The GPS receiver in your mobile device compares the time signals it receives from the satellites with its internal clock. Knowing the speed of light and when the signals were sent and received, your device can calculate your distance from each satellite, and thereby home in on your longitude, latitude and altitude.When was GPS first used? ›
Global Positioning System.
|First launch||February 22, 1978|
|Regime(s)||6 MEO planes|
The most common factors affecting GPS accuracy include clock errors, ephemeris errors, atmospheric delays, multipathing and satellite geometry. Clock errors occur because the previously mentioned internal timing circuitry of GPS re- ceivers is not as accurate as satellite clocks.
Recalibrate your Compass
To receive accurate directions in Google Maps, the compass must be calibrated. The problem may be due to the low accuracy of the compass. Even though the GPS is working properly, Google Maps will still show inaccurate navigation routes if the device's compass is not calibrated.
Limitations of GPS
Global Positioning Systems (GPS) are generally useless in indoor conditions as radio waves will be blocked by physical barriers, such as walls, and other objects. Also, regular GPS cannot pinpoint locations to greater than 3-m accuracy.
Is there an Alternative to GPS ? Yes, there is an alternative to GPS that is rising in fame, favorability, and calibre. It has been coined, VPS – 'Visual Positioning System' or CPS – 'camera positioning standard' by some. Rather than relying on geospatial referenced data, it works with images or visual data.What is Global Positioning System Class 9? ›
GPS stands for Global Positioning System. It is a radio navigation system used on land, sea, and air to determine the exact location, time and velocity irrespective of weather conditions. The US military first used it in the year 1960.What is the basic principle of GPS? ›
A global positioning system used for the purpose of navigation and detection of objects and places typically works on the basic principle of exchange of radio waves between the ground stations, satellites, and the receivers. This transmission and reception of data prefer a trilateration mechanism of operation.What is L1 and L2 GPS? ›
Each GPS satellite transmits data on two frequencies, L1 (1575.42 Mhz) and L2 (1227.60 MHz). The atomic clocks aboard the satellite produces the fundamental L-band frequency, 10.23 Mhz. The L1and L2 carrier frequencies are generated by multiplying the fundamental frequency by 154 and 120, respectively.What is the output of a GPS? ›
An output wire on a gps device, allows a signal to be sent from the device to an endpoint. Think of it as you being able to “energize” the output wire – and its like the wire saying – “Hey! I am sending a Signal Here, I'm On”. Two types of signals that you can send when you engage an output wire are latched or pulsed.What is better GPS or DGPS? ›
The basic difference between GPS and DGPS lies on their accuracy, DGPS is more accurate than GPS. DGPS was intentionally designed to reduce the signal degradation. GPS provides the accuracy about 10 meters, but DGPS can provide accuracy around 1 meter, even beyond that 10 cm.How does GPS calculate position? ›
A GPS receiver calculates its position by precisely timing the signals sent by GPS satellites high above the Earth. Each satellite continually transmits messages that include the time the message was transmitted and the satellite position at the time of message transmission.What can the GPS measured? ›
To calculate the Longitude, Latitude and Height position, a GPS receiver precisely measures the different speed of light (299,792 km/s) delays in the signals coming from 4 or more satellites. The distance to each satellite is calculated, and then using trilateration, the 3D position of the GPS antenna is calculated.
GPS technology is now in everything from cell phones and wristwatches to bulldozers, shipping containers, and ATM's. GPS boosts productivity across a wide swath of the economy, to include farming, construction, mining, surveying, package delivery, and logistical supply chain management.