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Section Three - Other Sources of Primary Data

Next to heads-up digitizing, collecting data in the field and importing into a GIS software is the second most common way to create new data. The ability to collect points, polylines, and polygons in the field in an efficient and accurate manner is an extremely important task in GIS. This task can be accomplished with high-dollar consumer mapping GPS receivers or, gaining in popularity due to a lower cost and a shallower learning curve, GPS collection apps for smartphones. Still in the heads-up digitizing category, but without the use of commercial GIS software,

6.3.2: GPS (Global Positioning Systems)

GPS units come in all shapes, sizes, and accuracies (and directly related, costs). They can range from thousands of dollars with real-time accuracy down to centimeters to a few hundred dollars with an accuracy of 10-50 feet. Just as GIS is a rather young science, the ability to collect quality data in the field with GPS units is just as new.

A Very Brief History of GPS Units

Selective Availability

Fearing military adversaries might use the GPS system to advantage, the Defense Department decides to deliberately decrease the accuracy of the system. By the early 1990s, civilians could buy GPS equipment that was accurate within only about 300 feet.

This inaccuracy was due to the deliberate distortion of the signal in order to prevent civilian gear from being used in a military attack on the U.S. This was called Selective Availability (SA).

On May 1, 2000, President Clinton signed an order ending SA as part of an on-going effort to make GPS more attractive to civil and commercial users worldwide. Now, GPS is accurate within 40 feet, or much better. Military GPS is even more precise and has a margin of error of only a few centimeters.

The end of Selective Availability was a major turning point that has helped GPS to become a global utility, now being used around the world in many different applications. After the attacks of September 11the, the industry buzzed over the possibility of a return to SA. However, on Sept. 17, 2001, the Interagency GPS Executive Board (IGEB), which governed the GPS system at that time, announced the United States has no intent to ever use Selective Availability again.



6.3.3: ArcPad, Field Maps, and Survey 123


ArcPad is a mobile version of ArcGIS which can be installed on a commercial mapping GPS receiver or tablet running Windows, providing many of the same features found in the desktop version. Most often, a GIS technician creates a geodatabase containing predefined feature classes and sets default values for the attribute table to make field collection a snap. For example, in order to send out a field crew ready to collect accurately and efficiently, the GIS technician will create a geodatabase containing a point feature class for trees with dropdown lists for the tress species, health, and size; a polyline feature class for trails with dropdown lists for the trail material type, trail width, and trail quality assessment; and a polygon feature class for large area invasive species with dropdown menus for species name, patch aggressiveness, and urgency to address the area.

Within ArcGIS, we predefine the dropdown lists of values utilizing the concept of geodatabase data domains, or a limited list of values that specific attribute table fields can contain. Geodatabase data domains can be either a list of user defined values (good, better, best; elm, maple, oak) or a range of values (1-10; 5-50). This method allows the field technician to collect features with attribute values more efficiently by using dropdown lists vs typing in the values one at a time with an on-screen keyboard. Imagine typing “Elm Tree” with a stylus on a tiny little digital keyboard 305 times a day! Hooray for geodatabase data domains!


Figure 6.9: ArcPad
arcpad_trimble arcpad_Screenshot
A Trimble GPS unit running ArcPad ArcPad Screenshot


Smartphone and Tablet Apps

Several free and low-cost apps are available for all the major smartphone and tablet operating systems (some better then others, obviously). These mobile GIS apps have done two things for the GIS community. First, they have put GIS into the hands of the “non-geo geek”, that is to say, those without some sort of formal or structured GIS training. Anyone who would like to make a map of their favorite running path can use an app as simple as “Map My Run”, or a more complex app such as Wolf GIS to begin to develop a complex online map showing not only their favorite running path, but terrain maps, weather patterns, and vegetation type polygons.

Second, many companies are beginning to ditch their expensive GPS units and replace them with cellular/wifi enabled GPS smartphones and tablets, as well as a more recent movement of tablets with true off-line GPS receivers. Plugin and Bluetooth GPS receivers can turn any smartphone or tablet into a field-ready GPS unit - with the additional benefits of a tablet such as word processors and electronic spreadsheets.

Esri, the makers of ArcGIS, have released a couple of smarthpone and tablet apps over the years, but more recently has developed and released two major apps: Collector and Survey 1, 2, 3. Collector is a version of ArcPad, and the trend seems to be that Esri is attempting to phase out ArcPad in favor of the very similar but multi-platform Collector. Instead of running on only a Windows based tablet or GPS receiver, Collector is a free1 app which runs on Windows, iOS, and Android, making it a more inviting choice for many companies and agencies. Currently, the features of Collector are not yet equal to those of ArcPad, which has a much longer development history in comparison.

Survey 1, 2, 3 is another multi-platform app from Esri more focused on use by citizen scientists. Even though the back end data creation and deployment is the same for the GIS technician, the end user doesn't need any experience with GIS to use the app. More focused on attribute collection via a from, Survey 1, 2, 3 can be used to collect data by a team of volunteers, such as raptor sightings, stream crossings, and items which may need to attention of a City Works department, to name just a few. Survey 1, 2, 3 is a bridge between GIS and the citizen, closer to crowdsourcing than to GIS data collection.

6.3.4: Crowdsourcing

Crowdsourcing is a method of data collection where the project designer turns the project loose on the internet community at large. Large scale projects which might be considered ‘impossible’ one one person or a small team of people, suddenly becomes attainable when a large amount of people contribute. In GIS and Remote Sensing, crowdsourcing is used to find points, polylines, and polygons in series of photos, such as burned buildings after a wildfire to assess damage, digitize missing roads after a major natural disaster to assist emergency workers, and helping to find missing airplanes.

Two geospatial crowdsourcing efforts are the Tomnod project and Open Street Maps. According the the Open Street Map website:

OpenStreetMap is built by a community of mappers that contribute and maintain data about roads, trails, cafés, railway stations, and much more, all over the world.

Local Knowledge: OpenStreetMap emphasizes local knowledge. Contributors use aerial imagery, GPS devices, and low-tech field maps to verify that OSM is accurate and up to date.

Community Driven: OpenStreetMap’s community is diverse, passionate, and growing every day. Our contributors include enthusiast mappers, GIS professionals, engineers running the OSM servers, humanitarians mapping disaster-affected areas, and many more. To learn more about the community, see the user diaries, community blogs, and the OSM Foundation website.

Open Data: OpenStreetMap is open data: you are free to use it for any purpose as long as you credit OpenStreetMap and its contributors. If you alter or build upon the data in certain ways, you may distribute the result only under the same license.

The Open Street Map Project

and the Tomnod website

Tomnod is a team of volunteers (like you!) who work together to identify important objects and interesting places in satellite images. Use Tomnod to explore the Earth, solve real-world problems, and view amazing images of our changing planet. With the help of millions of volunteer contributions, we fulfill our purpose of seeing a better world.

Tomnod Website

You can, with little to no GIS skills or experience, contribute to either project. You are encouraged at this point to visit the Tomnod site, set up an account, and spend a few minutes "arc minute" 1/60th of a degree. Usually denoted by " looking for the object at large. It’s really easy to do and an excellent introduction to digitization.