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Thematic Maps and Map Projection Utilities

A thematic map displays the spatial distribution of an attribute relating to specific data themes (e.g., population density, skin cancer mortality rates, rainfall, soil type, median age, number of housing units, pollutants concentration in air, etc.). Thematic maps provide specific information about particular locations.

Aabel allows creating thematic map diagrams that can display spatial data interactively using different options and easy to use customizing tools, and includes several importers as well as map projection utilities.

Importing Capabilities

Polygon and shape file data sets are readily available for download in the public domain. To enable importing and arranging polygon data, or defining the data using different projection systems, Aabel provides importers for:

  • ArcView shape files and associated dBase files
  • Formats provided by the USGS Coastline Extractor (such data can be extracted and downloaded from the NOAA/National Geophysical Data Center website):
    • Arc/Info Ungenerate
    • Mapgen
    • Matlab
    • Splus

Thematic Map Diagrams

Aabel allows plotting polygon thematic maps, polygon point frequency thematic maps, and polyline diagrams.

Polygon thematic maps: Allowing display of the associated data by:

  • Their values (see the right-hand side, top image below)
  • Their frequency or frequency percent
  • The number of selected data points
  • Categories belonging to a given attribute (see the right-hand side image)

Polygon point frequency thematic maps: Displaying data point frequency of X-Y coordinate pairs that represent occurrences of an item in different locations (see bottom images below).

A Thematic Map of Categorical Data

A Color- Coded Thematic Map of Frequency of Ozone Monitoring Sites

A Basic Thematic Map of Frequency of Ozone Monitoring Sites

Creating a Thematic Group Overlay

Combining a thematic map and one of the following charts can create a thematic group (see the image below):

  • A bubble chart, where X and Y being coordinates (easting-northing or longitude-latitude), and Z representing values of a data theme (see the left-hand side image below)
  • An X-Y vector chart, where X and Y being coordinates, and Z representing a direction using vectors (arrows)
  • An X-Y (scatter) pie, where the center of each pie has a unique X-Y coordinate (see the right-hand side image below)

Displaying Polygon Center Points

You can choose to display the center point of each polygon on a base map.

  • X-Y coordinates of polygon center points can be used in a scatter pie chart to produce a combination thematic map such as that in the right-hand side image below:

    The median family income by family size (in 2004 inflation-adjusted dollars); source of data: U.S. Census Bureau, American Community Survey (upper bound and lower bound based on 90-percent confidence intervals).

When creating a thematic group, the X-Y coordinates of the chart and the base map polygons must have the same projection system and data units. If your data require transformation, you can use the map projection utilities built into Aabel worksheets.

A Thematic Map of Population on Which the EPA 2006 Ozone Data Are Displayed

QuickTime Movies of How to Create Thematic Maps in Aabel

Creating a Polygon Frequency
Thematic Map (00.00:18)

Displaying Spatial Data
Dynamically (00.00:19)

Creating a Thematic Group
Overlay (00.01:57)

Operating on Selected Polygons

Integrated Map Projection Utilities

If the polygons are imported as numeric data with no explicit sample space, cartographic coordinate transformations are required to store the data as longitude-latitude or to define them using a different projection system. Aabel provides map projection utilities built into its worksheets to allow the following transformations:

  • Forward projections, which represent transformation of the spherical longitude-latitude coordinate system of the earth to the X-Y coordinate system of paper
  • Inverse projections, which allow you to transform the initially projected coordinates back to longitude and latitude

Aabel includes 19 projection systems, the geographic coordinate system, and the state plane coordinate system.

The supported systems include:

  • Geographic
  • Albers Conical Equal Area
  • Azimuthal Equidistant
  • Equidistant Conic
  • Gnomonic
  • Hammer
  • Interrupted Goode Homolosine
  • Lambert Conformal Conic
  • Mercator
  • Miller Cylindrical
  • Mollweide
  • Orthographic
  • Polar Stereographic
  • Polyconic
  • Robinson
  • State Plane Coordinate System (USA)*
  • Stereographic
  • Transverse Mercator
  • Universal Transverse Mercator (UTM)
  • Van der Grinten

    • * The state plane coordinate system is specific to US, and once a zone and the datum are selected, Aabel will automatically use the state-legislated projection and unit for that zone, as defined in NAD27 and NAD83.

You can execute coordinate transformation for any number of selected coordinate pairs rapidly, as shown in the image below: