Alternate Population Search Methodologies
As mentioned in the Population Estimator section, for radii of 25 miles or larger we will use census tract points as opposed to census block points to calculate the population. If you wish to look at a wider range of demographic data then users might use the following methodology.
This methodology applies principally to population around a defined point although it can be adapted to any of the methodologies that will be described below. In an unlocked layer, create a Reference Circle (Circle Tool) at a radius about a defined point. With the Reference Circle in Select mode, using the List Menu, Search for:
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Objects that are inside of or touched by the currently selected object; on the individual layer, Census Block Groups; on Maps in View.
When the Search is completed, use the Show All on Map button to return to map with the identified Census Block Groups in Select mode. It is obvious that the identified area extends well beyond the Reference Circle. To approximate a methodology known as Centroid Capture, do the following: While holding down the Shift key, click inside each Census Block Group that contributes less than half of its area to the Reference Circle. This deselects those Census Block Groups while retaining the remainder in Select mode. Retain all Census Block Groups that contribute half or more of their area to the Reference Circle. When the Census Block Groups roughly approximate the area of the Reference Circle, use Sharing/LandView/Get Info to view the informational attributes in LandView. The records for the first capture is displayed. A Summarize button displays the totals for the captured Census Block Groups for the Reference Circle.
Population within a defined polygon object
Place a polygon object (either pre-existing in MARPLOT or user created) in Select mode. Using the List Menu, Search for:
Objects that are inside of or touched by the currently selected object; on the individual layer, Census Block Points; on Maps in View.
When Search is complete, click on the button, Show All on Map. You are returned to the map with the identified block points in Select mode. In the Sharing Menu, use LandView/Get Info to view the associated information attributes in LandView. Data for the first object in the Search Collection is displayed. A Summarize button provides a summary of the population within the defined polygon.
Population residing within a sector of a circle
An unlocked layer is required, either the Temporary layer or one created for the purpose. With the layer unlocked, a reference circle can be placed at a defined point at a defined radius. (See Circle Tool) Define the sector of the circle by using the Polyline Tool to draw radii of the circle out and beyond the circumference of the reference circle. A message at the bottom of the screen displays the indicated angle from center. Now, using the Polygon Tool, create a defined polygon that mimics the created sector. From the center of the reference circle track one radius out to the circumference. Then, track along the circumference with two to four points (depending on the accuracy desired) and track the second radius back to close the polygon at center. Follow the procedure above for population within a defined polygon. Note: MARPLOT defines angle vectors to whole degrees only. A 22-1/2° sector cannot be created.
Population residing within a buffered polyline
(e.g., a noise pollution zone along a highway)
One or more polyline objects defining the proposed route are selected. Shift-Select allows multiple selection. Using the Edit Menu, Make New Polygon. For a polyline object, this creates a buffered polyline, actually a polygon, at a selected distance around the polyline. Using the methodology for Population within a defined polygon object, determine the population within the buffered zone. Note: Unrealistically defined buffers can lead to faulty conclusions. Display both the buffered polyline and the Census Block Points layer to preview results.
Source: U.S. Census Bureau
Last Revised: Thursday, 26-Jan-2012 15:38:32 EST