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Areas in ArcGIS Online

Revised 22 May 2026

Social and environmental phenomenon commonly occupy areas, which are portions of the surface of the earth enclosed by boundaries. In GIS, those areas are commonly represented with polygons, which are points at specific latitudes and longitudes that are connected with lines that define area boundaries. These areas can be large and formally-defined, such as nations, states, or provinces. They can also be small, as in property boundaries or building footprints, and the exact boundaries can be ambiguous, such as river flood plains or species habitats.

This tutorial covers mapping of areas in ArcGIS Online.

Polygons

An area is "a particular extent of space or surface" (Merriam-Webster 2020).

Areas are usually represented in GIS with vector polygons.

Polygons are formed by connecting node points at specific latitudes and longitudes with edge lines that form boundaries.

Curved boundaries are usually stored in GIS as polygons using closely spaced nodes that appear as curves when viewed. Conventional GIS data models do not have the ability to represent complex geometric representations (such as Bézier curves) that are available in graphic design programs like Illustrator.

Individual features sometimes consist of multiple polygons that are treated a single entity in GIS. In the example below, the border of England includes islands off the coast. In the second example, the country of South Africa wraps around the country of Lesotho, and the border of Lesotho is a second polygon carving out a hole in the contiguous area of the country.

Types of Areas

Getis et al. (2014, 14) defined a taxonomy of four different types of regions that expanded on Hartshorne's (1959) original three-part taxonomy. In the world of GIS, this taxonomy is useful for understanding these different types of areas and how information about them can best be captured, analyzed, and communicated.

• Administrative areas
• Formal areas
• Functional areas
• Vernacular areas

Administrative Areas

Administrative areas are areas that are "created by laws, treaties, or regulations" and are usually associated with government, military, or business control or operation (Getis et al. 2014, 14).

Administrative areas have clear, rigorously surveyed boundaries that are well-represented by discrete object polygons.

In the United States, there is a rough nested hierarchy of administrative areas that divide the country into areas that are managed by different levels of government:

• The nation is an area enclosed in country boundaries defined by international agreement.
• States are the 50 governmental areas in the US federal system with historically defined legal boundaries.
• Counties are the largest territorial division of states for local government in the US.
• Townships are area subdivisions of counties, and the organization of these varies by state. Townships are often associated with unincorporated areas of counties.
• Cities are municipal corporations incorporated and governed under a charter granted by the state.
• Wards and city council districts are subdivisions of cities often represented by officials elected from those wards / districts.

The US Census Bureau (USCB) is the part of the US federal government responsible for collecting data about people (demographics) and the economy in the United States. The Census Bureau has its roots in Article I, section 2 of the US Constitution, which mandates an enumeration of the entire US population every ten years (the decennial census) in order to set the number of members from each state in the House of Representatives (the lower house of the US Congress) and Electoral College (that selects the US President) (USCB 2017).

Numerous authors publish subsets of USCB data as feature services in ArcGIS Online. You should always use caution when accessing data from non-authoritative ArcGIS Online sources as the data is commonly work from student projects that is often of uncertain vintage and reliability.

The Minn 2020-2024 ACS feature service in the University of Illinois ArcGIS Online organization features a wide variety of commonly-used demographic variables from the 2020-2024 ACS five-year estimates data profile (DP) tables at state, county, and census tract aggregation levels. The data has full metadata and is also available as GeoJSON.

This layer uses scale-dependent rendering so that states, counties, or census tracts are displayed depending the level of zoom.

Formal Areas

Formal areas (uniform regions) are areas that each have a common set of physical or social characteristics.

Although Hartshorne's (1959) original taxonomy considered administrative areas to simply be a specific type of formal areas, this tutorial follows Getis et al. (2014, 14) in seeing formal areas as defined by their contents rather than by the decisions of governing authorities.

Unlike administrative areas that are rigorously surveyed and defined by the state, formal areas of both social and environmental phenomena often do not have geometrically simple, clear, and consistent borders, so the boundaries can be ambiguous and/or contested.

Physiographic regions are formal regions classified by common geological structures and histories (Fenneman 1917).

The ArcGIS Online Living Atlas of the World provides a layer of Named Landforms of the World which can be used for mapping physiographic regions.

Functional Areas

Functional areas (nodal regions) are focused on a central point, with diminishing influence the further you go away from that central point.

Metropolitan areas are functional areas that include "a major city together with its suburbs and nearby cities, towns, and environs over which the major city exercises a commanding economic and social influence" (Encyclopedia Britannica 2020). Metropolitan functional area boundaries often cross multiple city, county, and state administrative boundaries.

For tabulating purposes, the US Census Bureau defines a set of administrative areas as core-based statistical areas (CBSA) that include metropolitan statistical areas (big cities) and micropolitan statistical areas (small cities).

Although the USCB distributes information about metropolitan areas as clear boundaries in shapefiles, different types of influence (such as access to health care or commuting distances) can have different extents, and ties to the global economy can spread influence worldwide. Accordingly, you should interpret maps of functional areas with this ambiguity in mind.

For example, the Minn 2020-2024 ACS CBSA feature service in the University of Illinois ArcGIS Online organization contains selected demographic variables from the USCB's American Community Survey 2020-2024 five-year estimates for CBSAs.

Vernacular Areas

Vernacular areas (perceptual regions) are areas that are socially-defined by shared history and common identities (Wikipedia 2020).

An example of a vernacular area is a neighborhood, which is "a residential section of a city" (Merriam-Webster 2020).

• Neighborhood boundaries are inexact because they are defined by identities that are subjective and evolve over time under the influence of ethnic groups, real estate developers, and urban planners (city government).
• Neighborhoods grow and shrink based on time and social attitudes.
• Residents in adjacent homes may think of themselves as living in different neighborhoods even if there are no clear physical markers to indicate any difference between the neighborhood identity of their properties.

Google Maps displays neighborhood labels on major cities at a moderate zoom level. For example, panning north of downtown Chicago (The Loop), Google Maps shows neighborhoods named River North and Near North Side.

Types of Area Maps

A thematic map "is used to display the spatial pattern of a theme or attribute" ( Slocum et al. 2004, 1).

• Thematic maps contrast with reference maps (like Google Maps) that provide a general overview of information, often representing multiple variables.
• Base maps are reference maps placed under thematic map layers to provide geographic context.

Categorical Choropleth

A choropleth is a type of thematic map where areas are colored based on a single variable that describes some characteristic of those areas. Choropleths can be used to visualize both categorical and quantitative variables.

Categorical variables are names used to divide individual things into groups.

The following example creates a map of county-level winners in the 2012 US presidential election available.

• Add the Minn 2024 Electoral Counties feature service from the University of Illinois ArcGIS Online organization. The data was originally sourced from state secretaries of state offices, and metadata is available here.
• If needed, add a Filter for a single state (IL).
• Rename the layer (Winner 2012).
• Under Styles choose the categorical attribute you want to display (Winner_2012).
• Modify the Style options for Types (unique symbols) to change the colors if needed. In this case we use the standard highly-saturated red / blue palette common for maps of this type in the media since 2000.
• Under the Properties, Appearance, Blending, select Multiply so the choropleth colors the base map and allows the base map symbols to be visible through the choropleth polygons.

Classified Choropleth

Choropleths can also be used to visualize quantitative variables.

Quantitative variables represent characteristics as quantities or numeric values.

To make it easier compare and contrast groups of similar values, quantitative variables are often classified into ranges of values (classes) that are assigned to a limited number of different colors.

A diverging color scheme uses a range of colors between two opposite hues separated by a neutral color like white or gray. The use of the two different hues makes it easier to distinguish between areas with lower and higher values while still being able to see intermediate values between the extremes of the range.

This example uses the percentage of the Democratic vote in the 2012 election.

• Duplicate the counties layer added above and rename the layer (Percent Democratic 2012).
• Under Styles choose the quantitative attribute you want to display (Percent_Dem_2012).
• Select Counts and Amounts (color) with a High to low diverging color scheme.
• Under Style options select Classify data. The default of Natural Breaks (Jenks) is usually a safe method.
• Under the Properties, Appearance, Blending, select Multiply so the choropleth colors the base map and allows the base map symbols to be visible through the choropleth polygons.

Graduated Symbol Maps

One approach for mapping quantitative values for irregularly sized areas (like states) is to use a graduated symbol map rather than a choropleth. A common example of this is the "bubble" map that uses differently sized circles based on the variable being mapped. Although circles are most common, other types of icons can be used for aesthetic variety.

Graduated symbol maps are also more appropriate than choropleths when mapping counts rather than amounts (rates). Counts are variables that indicate size, such as the size of the population. With choropleth maps our eyes see the land area as the size, and when the sizes indicated by the variable are not the same as the sizes of the areas, we get an incorrect impression of where the larger and smaller values are located.

1. Duplicate and rename the layer (Democratic Votes 2012).
2. Under Styles choose the quantitative attribute you want to display (Votes_Dem_2012).
3. Choose Style options for Counts and Amounts (size) with an appropriate color and bubble size scaling as needed.

The Modifiable Areal Unit Problem

The modifiable areal unit problem (MAUP) is "a source of statistical bias that is common in spatially aggregated data, or data grouped into regions or districts where only summary statistics are produced within each district, especially where the districts chosen are not suitable for the data" (wiki.gis.com 2022).

For example, maps of electoral results give a very different impression depending on whether you map by state or by county.

There is no universally applicable solution to the MAUP. In cases where accuracy is not essential (such as with data exploration) or possible (such as with data that has been aggregated for privacy reasons), the uncertainty presented by the MAUP may be acceptable as long as caveats are provided along with the analysis. In other cases, more-sophisticated analytical approaches may be more appropriate.

In drawing electoral boundaries, gerrymandering is an intentional political use of the MAUP where specific groups of voters are either "packed" into a small number of homogeneous districts or "cracked" across multiple districts in order to reduce the power and representation available to those groups.

You can create a map of a gerrymandered district using the Minn 2024 Electoral Districts feature service in the University of Illinois ArcGIS Online organization.

Exclusive Visibility

Exclusive visibility layer grouping permits the user to only select one layer at a time in map layer controls for layer viewing. Exclusive visibility can be useful with multi-layered maps when displaying multiple layers at one time would cause visual conflict.

• Select one layer and choose Group.
• Drag the rest of the layers into the group.
• Under the group Properties, choose Exclusive visibility.
• If you are using multiply blending, set the blending mode for the group.