An Example of Local Government Using GIS (2 of 30)

By | October 19, 2021

As the “2 of 30” in the title implies, this post is part of an ongoing series discussing Missouri Revised Statute § 67.1850. (If you haven’t read it yet, you may want to go to the first post in the series: Introducing Mo. Rev. Stat. § 67.1850 (1 of 30).) The purpose of this second post is to share some nuts and bolts about GIS. You might decide to skip it if you’re already an expert, but I encourage everyone else to keep reading. First up in this post, I give you a brief idea of how officials working for local governments, specifically county appraisers, capture and use GIS data. Second, I explain the main elements in a GIS data set (expressions, attributes, and layers). Third and finally, I describe how some people choose to use the data that government officials collect and share with the public.

A geographic information system (GIS) is comprised of (1) the people who operate the system; (2) the GIS software used to manipulate (3) the GIS data, which is often called spatial data; and (4) the electronic computing, input, storage, transmission, and output devices associated with GIS.[1] GIS can be considered a computing tool used to manage information that has both a location and one or more additional attributes.[2] It simplifies the mathematical equations involved in provided geospatial information.[3]

How County Appraisers Collect and Use GIS

Missouri county appraisers check and note—among many observations—whether new construction has occurred over the past two years in their jurisdiction.[4] Their goal is to ensure that all property may be fairly and appropriately assessed for property tax purposes.[5] In two years’ time, a county’s appraisers will drive every road in their jurisdictions, making complex notes for entry into the county’s tax appraisal system, which may also be a GIS system.[6] As she drives, an appraiser will make notes and match addresses and photos of assigned properties to photos from prior years.[7] If she is in a county with the most up-to-date technology, she collects data on a location-enabled camera, which determines its location and the direction it is being pointed by using the array of twenty-four satellites in the United States GPS.[8] Her location and that of the building she is appraising is accurately known.[9] As she is taking photographs, the system records her voice notes about the condition of the property and stores that sound file in a way that links the file to the location where she dictated her note.

Once back at the office, she downloads the date she collected into the county’s GIS system. Upon download, the system knows where each building is located and which buildings are in which photos. It also translates her voice notes to text. This location-enabled camera permits the assessor to conduct her job faster and with less error.[10] Ostensibly, every record she makes is a public record under the Missouri Sunshine Law—or is it?[11]

Geographic Expressions

The geographic portion of GIS provides information about mapped subjects. Location is in turn described as one of three types of feature classes—each with its own topology.[12] Feature classes include (1) points, (2) lines, and (3) polygons. In addition, some authorities include raster data.

Raster data contains attribute data, which combines with location information to form a digital map of our physical world.[13] The first feature class, a point, is a “geometric element defined by a pair of x,y coordinates.”[14] A point feature may be a “map feature that has neither length nor area at a given scale, such as a city on a world map or a building on a city map.”

A line is the second feature class, which, “[o]n a map, is a shape defined by a connected series of x,y coordinate pairs. A line may be straight or curved.”[16] Further, a line may be a “feature that has length but not area at a given scale, such as a river on a world map, or a street on a city map.”[17]

A polygon is the third and last feature class, which, “[o]n a map, [is] a closed shape defined by a connected sequence of x,y coordinate pairs, where the first and last coordinate pair are the same and all other pairs are unique.”[18]

The boundary of a single lot in a residential subdivision is a polygon. However, it’s important to note, raster topology combines spatial location with attribute data in an altogether different way than points, lines, and polygons describe the same geography. A raster is a “spatial data model that defines space as an array of equally sized cells arranged in rows and columns, and comprised of a single or multiple bands. Each cell contains an attribute value and location coordinates.”[19]

For example, Figure 1 shows a six-by-six array with a range of sixteen shades of gray for each cell or raster.[20] Values range from 1 being the lightest to 16 the darkest. Each cell’s location is also described by its x,y position within the raster array.  Aerial photography is an example of raster data.[21]

Attributes: All Topology Forms May Have Them

What makes a GIS more than just a digital mapping system is its ability to link each polygon, line, and point to a collection of attribute data. Attribute data is “[n]onspatial information about a geographic feature in a GIS usually stored in a table and linked to the feature by a unique identifier.”[22] For example, if the geographic location of every fire hydrant in a community is known, that list can be linked to a table containing attribute data. In Tables 1 and 2, the light-blue cell shading indicates the necessary matching data field that the two tables have in common. Like most database operations, having a data field in common allows data to be joined.[23]

Layers: The Union of Attribute and Geographic Data

A dataset, or layer, is GIS data with a single theme. For example, a layer may contain every water well location in the state with attribute data, which might include the date of drilling, well driller’s license number, and the depth of the well. This type of layer may be as simple as a spreadsheet. Fire hydrants (point), streets or water lines (line), and parcels or precinct voting wards (polygon) are all examples of commonly produced layers held by a local government.

GIS Data Storage

GIS information can be stored in a number of ways, but it’s most often stored with the layers organized by the bounded area covered or organized by the level of government the data describes. County street layer data, for example, rarely exceeds the boundary of the county, and Missouri state parks are rarely found in adjoining states. Thus, relying on boundaries, GIS data is stored in a logically organized manner, just as if it were any other collection of records.

Alternatively, GIS data may be stored in a proprietary database. In this situation, the software manufacturer allows the GIS technician to feed data sets into the database where the data remains unrecognizable and unidentifiable to a casual user browsing the data with a file manager or file explorer program.

The Systems Aspect of GIS

GIS technicians, the people working in the system, range widely in both education and experience. A typical entry-level GIS position requires a bachelor’s degree in one of the associated fields [24] and several hours of GIS coursework as an undergraduate. Recently, a number of Doctor of Philosophy (PhD) programs have been established to support the geospatial sector’s desire for even more highly educated professionals.[25]

While GIS software may be obtained from open-source software providers, the majority of users at the government level purchase one of the numerous commercial software packages available.[26] The largest commercial GIS software market share is held by Esri, which is estimated to have between 40% to 50% of the total commercial market and a much higher ownership of the state and local government markets.  

In recent years, a proliferation of GIS software has been developed for platforms beyond the traditional computer workstation. GIS software is now used from survey devices like Total Stations™, GPS receivers, smartphones, tablets, laptops, and, most recently, with the deployment of Google Glass, GIS via eyeglasses.[27]

Location information is assembled from anyone or anything taking geographic measurements and recording attributes. Activities are as varied as engineers surveying the location of a future road, surveyors mapping out a subdivision’s corner pins, technicians matching aerial photo pixels or satellite imagery to known ground locations, and even hikers uploading their day’s trek. The latest developments allow individuals, drones, aircraft, and satellites with location-enabled devices to add location and attribute data to a crowdsourced map.  

Similarly, attribute data is assembled from a variety of sources. For instance, the state of Missouri has a database containing a record of the name, address, and all other necessary information for it to properly license every professionally licensed health care worker and facility in the state.[28] In this database, addresses are matched to their corresponding geographic locations through a process called geocoding.[29] Anyone with GIS software and this database can display the spatial distribution of every doctor’s office in Missouri.[30] 

For example, a doctor specializing in gerontology might use that same Missouri Physicians GIS layer to select and display only Missouri gerontologists from all licensed health care providers viewable in the layer. The doctor may then display those specialists over the next map layer, which is made to show the latest United States Census data on existing and projected elder populations. This analysis can yield very useful information for a doctor looking to start a specialty practice. 

Next, with a few intelligently structured commands given to the GIS software, our good doctor might be able to mathematically classify multiple areas of the state by the number of potential patients, their average income, and the number of gerontologists practicing within thirty miles.  

Information can be placed into a GIS by many different methods. First, information may be loaned, given, or purchased preformatted for use by the GIS. Second, information can be entered into spreadsheets manually—through a variety of techniques—and then manipulated into a GIS readable format. Third, information can be entered automatically by devices, like a GPS receiver, or with a laser rangefinder as used by land surveyors. Finally, information can be created by manipulating one or more existing data sets to produce a new GIS data set.

GIS data can be distributed in a raw form (text or code) or more processed form. In the raw form, it may be printed out, copied digitally, or made available for download over the internet. In a processed form, GIS data may be displayed as a finished printed map product, projected through a speaker as verbal driving directions, or viewed from within an internet web browser. There are no significant limitations as to how GIS data may be shared, which distinguishes GIS data from any other publicly held data sets.

Physical storage of GIS data may involve a number of media storage types and methods. First, GIS data can be stored on a local hard drive, on a local or remote network, or archived for later use. Thus, GIS data sets are stored like any other data set, and, like other data sets, they are organized with some type of logical hierarchy in place. Alternatively, GIS data may be stored within a proprietary geodatabase, which is a “collection of geographic data sets.”[31] To extract a single data set from a geodatabase, such as a copy of the county road data set, requires the use of the same proprietary GIS software that assembled the geodatabase. However, no matter how the GIS data sets are stored, they are routinely copied and backed up in all of the common ways.

GIS data do not greatly differ from other electronic records held by a local government. The only real difference between GIS data and the rest of a government’s digital records is that GIS data have been organized in a way that allows GIS software to quickly access and manipulate these records. Often the GIS system holds the only copy, other than back-up or archives, of an entire set of government records. It is commonplace for property records, other than deeds and similar archival documents, to be kept primarily within GIS format.

GIS data can be viewed in two distinct ways. One way is to utilize the vertical view, where a GIS user is able to “look down” through several data sets much like looking at a map with a rich set of features. By using the vertical view, the GIS user can turn on and off layers to suit their needs and see the relationship between different layers. A person using an online GIS web browser could turn on each of the layers he or she desires to view and then zoom in or out to view the map at the desired scale; for example, a person can view just his or her neighborhood. However, the user could not examine the full extent of one layer in detail by looking at all of its attribute data because that requires a horizontal view—the second and alternate viewing method.

A horizontal view is akin to examining the entire data set and its attributes. A GIS user would want to use this view to see patterns, gaps, omissions, overlaps, duplicate records, or any other spatial aspects of the data. An online GIS browser does not allow the user to utilize a horizontal view. To obtain a horizontal view, one needs the entire data set. Additionally, one can look at multiple data sets and discover new relationships by viewing two or more data sets horizontally. Some communities make both vertical and horizontal views available.[32]

The city of Columbia, Missouri, for example, offers an online map that permits citizens to view a variety of GIS layers, or download several layers to view an entire layer’s attribute data all at once.[33] The ability to view an entire layer all at once is important to those seeking to leverage GIS’s transparency powers.


[1] This is an amalgamation of various definitions found across the GIS sector.

[1] Herzog, supra note 4, at 20.

[2] See, e.g., Overview, Esri, (last visited August 21, 2019) (explaining that “[a] geographic information system (GIS) integrates hardware, software, and data for capturing, managing, analyzing, and displaying all forms of geographically referenced information. GIS allows us to view, understand, question, interpret, and visualize data in many ways that reveal relationships, patterns, and trends in the form of maps, globes, reports, and charts. A GIS helps you answer questions and solve problems by looking at your data in a way that is quickly understood and easily shared. GIS technology can be integrated into any enterprise information system framework.”).

[3] See Geographic Data, Esri, (last visited August 21, 2019) (defining “geographic data” as “[i]nformation describing the location and attributes of things, including their shapes and representation. Geographic data is the composite of spatial data and attribute data”). See also, Wade & Sommer, supra note 2, at 212 (defining “topology” as “[i]n geodatabases, the arraignment that constrains how point, line, and polygon features share geometry”).

[4] Mo. Rev. Stat. § 137.115 (2013).

[5] The Role of Property Assessment in Missouri, Missouri State Assessors Association, (last visited August 21, 2019) (stating “the role of the county assessor is to keep track and value all of the real estate and tangible personal property in their county. Property valuations are based on market value per the Missouri Constitution and the system of annual assessment on personal property and biennial (every two years) assessment (a.k.a. reassessment) on real estate is per Missouri Statutes.”).

[6] Land Administration, Esri, (last visited August 21, 2019) (explaining Esri’s integration of ArcGIS with Computer-Assisted Mass Appraisal (CAMA) systems).

[7] The Assessment Cycle, Missouri State Assessors Association, (last visited August 21, 2019) (explaining that the “2 Year Maintenance Plan [requires] each county … to develop and follow a comprehensive two-year assessment maintenance plan agreed upon by the county assessor, the county commission, and the State Tax Commission. The plan covers all aspects of the assessment process, the two-year time frame covering each reassessment period.”).

[8] Space Segment, Constellation Arrangement,, (last visited August 21, 2019).

[9] See Appraisal,, (last visited August 21, 2019) (providing a tour of the technology being used to make appraising easier and more efficient.).

[10] Best Practices for Local Government Geospatial Programs, National Geospatial Advisory Committee *3 (2011), available at (explaining “[g]eographic information system (GIS) technology provides vital support for almost everything the local government does. Well-defined geospatial programs help jurisdictions provide quality service to citizens in a cost effective manner.”).

[11] § 610.010.

[12] See Wade & Sommer, supra note 2, at 212 (defining “Topology” as, “[i]n geodatabases, the arrangement that constrains how point, line, and polygon features share geometry. For example, street centerlines and census blocks share geometry, and adjacent soil polygons share geometry. Topology defines and enforces data integrity rules (for example, there should be no gaps between polygons). It supports topological relationship queries and navigation (for example, navigating feature adjacency or connectivity), supports sophisticated editing tools, and allows feature construction from unstructured geometry (for example, constructing polygons from lines).”).

[13] Id. at 175 (defining “raster” as “groups of cells that share the same value represent the same type of geographic feature”); id. at 11 (defining “attribute” data as “[n]onspatial information about a geographic feature”).

[14] Id. at 163.

[15] Id.

[16] Id. at 123.

[17] Id. at 124.

[18] Id. at 164.

[19] Id. at 175.

[20] Note

[21] Id.; see also id. at 11 (defining “attribute”).

[22] Id. at 11.

[23] Id. at 115 (defining “join” as “appending the fields of one table to those of another through an attribute or field common to both tables. A join is usually used to attach more attributes to the attribute table of a geographic layer.”).

[24] Associated fields include geography, geomatics, geology, archeology, urban planning, engineering, engineering technology, and others.

[25] See The GIS PhD Dilemma, Directions Magazine (2008), (last visited August 21, 2019).

[26] ArcGIS Desktop 10.2.2, Indiana University (Mar. 25, 2014), (explaining “ArcGIS for Desktop is used to compile, use, and manage geographic information. It includes a comprehensive set of professional GIS applications that support a number of GIS tasks, including: mapping, data compilation, analysis, geodatabase management, and geographic information sharing. The ArcGIS 10.2.2 setup package is designed to detect and upgrade an existing installation of the same ArcGIS 10.1 (including Service Pack 1 [SP1]), 10.2 or 10.2.1 product. The settings for the installation location, license manager (for Concurrent Use), or authorization information (for Single Use) are retained in the upgrade. See the installation guide for more information on installation upgrades, new installations, or installations over versions prior to 10.1.”).

[27] See GLASS,, (last visited August 21, 2019).

[28] See Missouri Spatial Data Information Service, (last visited August 21, 2019).

[29] Wade & Sommer, supra note 2, at 84 (defining “geocoding” as “[a] GIS operation for converting street addresses into spatial data that can be displayed as features on a map, usually by referencing address information from a street segment layer”).

[30] Id.

[31] See Michael Zeiler, Modeling Our World (1999), which states, “A Geodatabase is a top-level unit of Geographic data. It is a collection of data sets, feature classes, object classes, and relationship classes.”

[32] Many communities in Missouri offer vertical views through online map views where the user can turn on and off layers. CITE But without access to the horizontal view, which is access to the entire data set—as well as access to the query tools inherent in GIS software—much of the power of GIS to provide transparency is lost. CITE?

[33] Welcome to Map Source, City of Columbia, Missouri, (last visited August 21, 2019).