1. Location and Attribute Queries
TransCAD
Location and Attribute Queries
2018/11/15

2. Location and Attribute Queries
TransCAD provides many tools for asking and answering questions about the features in a map and the data in a dataview. These tools answer three types of queries:
Location questions: “Which commuters live within 1 mile of a train station?”
Attribute questions: “Which airports have more than 1,000,000 enplanements per year?”
Combination questions: “Which highways in Connecticut have a speed limit of 65 miles per hour?”
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3. Answering Questions about Location
A location question is used to find map features that are located in a particular area. For example, which customers live within 5 miles of a store?
To answer a location question, you use either of two methods:
Select features directly from a map with the selection tools
Select features by location relative to features in another layer
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4. Select Features with the Selection Tools
If you want to include features that are partially contained in your selection set….
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5. Select Features Directly from the Map
Click on a single feature, or drag a rectangle to select all features inside the rectangle.
Drag a circle to select all features inside the circle, or click at the center of the circle and type the radius in the Enter Selection Radius dialog box.
Draw an area to select all features located inside the area. Click on each corner of the area, and double-click to close it.
Clear the selection set so that no features are selected.
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6. Select Features by Location
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7. Answering Questions about Attributes
A question about attributes is used to find records that meet a certain condition. For example: which ZIP Codes have an average household income of over $40,000 per year?
You use the Selection-Select by Condition command to select records and map features whose values meet a condition.
Conditions can contain field names, arithmetic operators like +, -, * and /, relational operators like <, >, <=, >=, and <>, and many different types of numeric and string functions.
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8. Answering Questions about Attributes
The Selection-Select by Value command lets you select features in a working layer based on a value in a field for another layer, the reference layer.
If you want to find:
The workers whose workplace is in one of several ZIP Codes, select those ZIP Codes and then select the workers based on the ZIP Code of their workplace.
The counties in a state, select the state and then select the counties with that state’s name or code.
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9. Select Based on a Condition
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10. Select Based on a Value
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11. Create Selection Sets from a Theme
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12. Managing Selection Sets
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13. Showing Selection Sets in a Dataview
Click on it to select or remove from a selection set
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14. Highlight Selected Records in a Dataview
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15. Combining Selection Sets
Sometimes you want to combine a location question with an attribute question. For example, “Which block groups are not near subway stations, but are still home to a large percentage of subway commuters?”
To answer this kind of question, you can combine two other selection sets.
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16. Combine Selection Sets
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17. Creating New Files from Selection Sets
You select records from a geographic file because you want to highlight them in a map or produce a tabular report showing records that meet some condition. TransCAD also lets you take the records in a selection set and create new tables or new geographic files that contain only those records.
From a selection set, you can save a:
Dataview to a new file on disk that stores information only for the records in a selection set.
Geographic file that contains only the selected map features. The new geographic file is smaller than the original, of course, and contains fewer features.
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18. Create a New Table from a Selection Set
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19. Create a New Geographic File from a Selection Set
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