1. Using Themes to Present Information
TransCAD
Using Themes to Present Information
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2. Themes
TransCAD can assemble information about map features to create a map that illustrates the patterns in the data. This is called a thematic map.
Thematic maps use distinctive colors, symbols, and fill styles to portray data such as population, rainfall, sales, or income. The different styles highlight the similarities and differences among map features.
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3. Themes
Thematic maps illustrate the characteristics of map features, so that the characteristics are easy to see and understand. TransCAD has six theme types:
Color themes
Pattern themes
Dot-density themes
Pie and bar chart themes
Scaled-symbol themes
Prism maps
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4. Deciding which Type of Theme to Use
To illustrate the values of a single field, you can choose from all five theme types, using the following guidelines:
Counts or amounts (Population, Sales) – Use any kind of theme
Percentages, ratios, or averages (Avg. Income, % Hispanic) – Avoid dot-density themes
Negative number (Change in Population) – use color or pattern themes
Non-numeric information (Zoning, First Name) – Use color or pattern themes
You choose the theme you want based on the number of fields of data you want to show and the types of data you wish to present:
Most theme types can be used with any point, line, and area layer.
Dot-density themes and prism maps, however, can only be used with area layers.
To illustrate the values of two or more fields, choose between using a chart theme and a dot-density theme.
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5. Color and Pattern Themes
Color themes and pattern themes work in the same way. They both group the features in a map layer into classes, based on the value of a data field. Each class contains all of the features with similar values for the chosen field.
When the map is drawn, the classes are displayed using different colors or patterns.
When you create a theme using a formula field instead of an existing data field, TransCAD adds the formula field to the layer.
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6. Create a Color Theme from a Dataview
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7. Add a Pattern Theme to a Map
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8. Change, Turn Off Color/Pattern Theme
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9. Options
Method
Equal number of features: Each class has the same number of features.
Equal size intervals: Each class has the same range of numbers.
Equal feature area: The total land area of features in each class is about the same. It can only be used for area features.
Equal feature length: The total length of features in each class is about the same. It can only be used for line features.
List of values: Each value is assigned to a separate class.
Standard deviation: Features are split into classes for a number of standard deviations above and below the average value. Type the number of standard deviations in each class in the options box.
Nested averages: Features are split into two classes based on the average value. Each of those classes is split in two based on the average value for features in the class, and so on. This method creates either 2, 4, 8, 16, 32, 64, 128, 256, or 512 classes.
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10. Manual
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11. Dot-Density Themes
A dot-density theme uses dots or other symbols on the map to show the values of one or more numeric data fields. Each dot on a dot-density map represents some amount of data.
Dot-density themes can only be created on an area layer, such as ZIP codes, TAZs, census tracts, or sales districts.
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12. Create a Dot-Density Theme
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14. Pie and Bar Chart Themes
Pie and bar chart themes place pie or bar charts on map features to illustrate the data that go with each feature.
TransCAD has 5 chart styles from which you can choose:
Pie chart ( 3-D not available)
Vertical Bar Chart
Stacked Vertical Bar Chart
Horizontal Bar Chart
Stacked Horizontal Bar Chart
Chart themes can be created on point, line, and area layers.
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15. Create a Chart Theme from Dataview
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17. Add a Chart Theme to a Map
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19. Scaled-Symbol Themes
A scaled-symbol theme uses symbols of different sizes or lines of different widths to show the value of a data field.
Scaled-symbol themes can be created on point, line, or area layers. On line layers, the lines are scaled in width based on the value for the chosen field. On point layers, the symbol that is used to display the point is scaled in size based on the value of the chosen field. On area layers, you choose the symbol you want to use, and TransCAD displays the symbol at the center of the area, scaled in size based on the value of the chosen field.
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20. Scaled-Symbol Themes
TransCAD has a special dual-bandwidth feature for line layers that lets you see data that vary by direction. This feature can be used to show many different types of data, for example:
The number of cars traveling in both directions on a street network
The capacity of a transit line in passengers per hour
Highway pavement width
Commodity flows along rail lines
The layer must contain two fields that indicate the value of the field in each direction along the link.
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21. Add a Scaled-Symbol Theme to a Map
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23. Prism Maps
A prism map uses 3-D imaging and color to show the relative values of a single data field. Prism maps can only be created on an area layer, such as counties, states, or sales districts.
There are two important differences between prism maps and the other types of themes:
TransCAD creates a prism map in its own figure window alongside your current map.
TransCAD reads the data for a prism map when the prism map is created, so subsequent changes in the data are not reflected in the prism map. To have those changes reflected, you must recreate the prism map.
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24. Create a Prism Map
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26. Customizing a Prism Map
TransCAD allows you to customize a prism map in a variety of ways:
Add customized titles and footnotes
Change the initial height and the angle at which it is viewed
Add a legend
Apply logarithmic scaling to your data
Change the colors by selecting a predefined color set or by using the color ramp
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27. Coloring a Map
Edge: Assign a color to every area, making sure that no areas that share a common border have the same color.
Node: Assigns a color to every area, making sure that no areas that share a common border or node have the same color.
Island: Assigns a color to every area, making sure that no areas that share a common border or node, or are separated by a body of water, have the same color.
The Map-Coloring command assigns color codes to areas, or uses existing color codes, and creates a color theme that displays the layer with areas next to each other having different colors.
There are several adjacency methods that you can use for coloring a map:
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