TAP Data Summation Function

Q: Can I use TAP 5 to count information in shapefiles in my coverage area?

A: For TAP 5.0.1030 systems with a Maintenance Subscription date of November 30, 2004, or later, TAP Coverage studies and other polygon layers can be used to summarize data values (such as population counts) in SoftWright’s HDMapper program.

Note that all values shown in this article are for illustration purposes only. It is important that you use good engineering judgment to determine the values that are appropriate for your equipment and specific application.

Population counts are one common use of the more general Data Summation function available in HDMapper. Population counts are provided as a separate function as described in other FAQs.

□ Tile Coverage Population Counts

□ Contour Coverage Population Counts

□ Aggregate Coverage Population Counts

If you want to use a TAP coverage study (Tile, Contour, or Aggregate Coverage) for the data summation process, you must first setup and run the coverage study and plot the coverage area with HDMapper. If you want to use another shapefile layer for the selection of data to count, you must add that layer to the map.

The shapefiles created by TAP coverage studies run with earlier versions of TAP (before TAP 5.0.1030) cannot be used with the population count function. You do not need to run the study again, but you can use the TAP “Export Coverage to Shapefile” function to create a new shapefile with the new version of the software. This new shapefile can be used for the population count. (For Tile or Aggregate studies, be sure to select “Write rectangles” in the Export function for the type of file to write.)

You should be sure the layer(s) you want to use are included in the map. The layers can be included automatically with the “Set TAP5 Default Layers” function, or you can add layers to the map manually.

Layer Types

The basic function of data summation (including population counts) in TAP is to use one layer consisting of one or more polygon objects as the “selection layer.” Data contained on other layers as point objects can be selected as the items to count. The data summation process finds all the objects to be counted that fall within the polygon(s) on the selection layer. The program reports the total of the counted items.

Examples of polygon layers include:

□ TAP Contour Coverage studies – one polygon representing a contour computed for a specified field strength level

□ TAP Tile Coverage studies – numerous polygons representing various field strength levels computed for points on a rectangular grid. The program can select a range of field strength values to use for the count selection, only counting the points that fall in tiles with a certain field strength range.

□ County or other areas, including your own shapefiles or shapefiles you obtain from other sources.

Examples of point layers include:

□ USGS Census info, such as Block Centroids that contain population totals for small block areas

□ City summary files, such as points that represent a reference point for a city or large area and include summary demographic information for the area.

Data Granularity

It is important to consider the resolution or “granularity” of the point data to be counted in a data summation.

For example, consider the example shown below.

This illustration shows the approximate city outline of the city of Fort Collins, Colorado.

Adding, for example, the CO_cities (Colorado cities) layer, causes the city reference point from that shapefile:

The CO_cities layer is a summary of demographics for the entire city. Using this kind of layer for counting information should be done with great care.

For example, consider a coverage contour that you want to use for counting information in the Fort Collins area:

In this case, the reference point for Fort Collins is just outside of the coverage contour, and therefore would not be included in the count.

However, a different contour (maybe computed with a different power or antenna height, etc.) could yield quite different results:

In this case, the city reference point for Fort Collins is just inside the contour, so the entire population (or other demographic) for Fort Collins would be included in the count. Clearly, from the Fort Collins boundary line shown on the map, this would not be a good estimate of the coverage for this area.

A better approach is to use data with higher resolution, or better “granularity”. Adding the CO_Block_Population layer (from USGS Census Block data), offers a better use of the data summation function:

The more granular data is based on block counts instead of a summary for the entire city. As an illustration, this example yields a population count of 51,947 for the smaller contour, and 73,140 for the larger contour. This more granular point data gives a more realistic representation of the differences between the contours. The “all or nothing” approach using the summary reference point may distort the differences.

Anytime you are using summary data for an entire city or large area, you should exercise caution in interpreting the results. If possible, always try to use data with smaller units for better resolution. Population counts (which are a specific subset of the Data Summation function), use only Block Centroid point shapefiles.

Data Summation Setup

Suppose you have two custom shapefiles:

□ Target Service Area that defines an area of interest to you

□ Sample Points that contains information you want to count

When these desired layers have been added to the map, click the “Data Summation” button:

The Data Summation form will be displayed:

Layer to Use

First, use the pulldown “Layer” list to choose the layer you want to use as the area to count. In this example, you would select the Target Service Area layer:

(Note in the more specialized Coverage Population Count functions {Tile, Contour, Aggregate Coverage} only layers consisting of field strength calculations computed with TAP will be displayed. The Target Service Area layer would not be displayed using the Coverage Population Count functions.)

Data Field to Use

Next, select the data value field to use. For this example with this hypothetical shapefile, select the field “AREA_NAME”:

(Note in the more specialized Coverage Population Count functions {Tile, Contour, Aggregate Coverage} only the fields containing recognized field strength information, such as the DBU_FIELD values, are available. The AREA_NAME field would not be displayed using the Coverage Population Count functions.)

Data Field Range or Objects

When the data field is selected, the number of values on the layer is shown.

□ If the data field is a numeric type (as in the case of the DBU_FIELD data for coverage population counts, the range of values is also shown.

□ If the data field is a character type (as in the case of this hypothetical Target Service Area file, the name of each object in the file is displayed.

You can use the check boxes to select which object(s) you want to use for the count. The polygon objects you select will define the area where the program will search for items to count. In this example, only the Target Service Area will be selected:

If the data field selected is a numeric type field, the value range will be displayed. For example, suppose you selected the “Priority” field for this layer:

The range of values will be displayed. You could select the range of values to include in the counting area. The initial default values are the minimum and maximum values found in the layer.

For this example, we will use the AREA_NAME field originally selected, so you could select AREA_NAME from the pull-down list:

Click the Target Service Area box to use that object for the count:

Layers to Count

Determine the layer(s) you want to count. For Coverage Population counts, the layers listed only included those layers that are recognized as containing population information, such as the U.S. Census Block Centroid layers.

(Note in the more general Data Summation function all “point” type layers are displayed and you can select data fields in any of the layers.)

Fields to Count

Select the data field(s) you want to count in each layer by marking the checkbox for that data field. For Data Summation counts, the fields listed include all numeric fields in each layer. For this example, you could select the hypothetical “OWL_NESTS” field:

(Note in the more specialized Coverage Population Count functions {Tile, Contour, Aggregate Coverage} only the fields containing recognized population, such as the POP100 values in census Block Centroid files, are available. The OWL_NESTS field would not be displayed using the Coverage Population Count functions.)

Sum All Values

If more than one data field is to be counted you have the option to sum all the fields by marking the “Sum all values” checkbox.

For population counts, only population fields are available for counting, so summing all the values is a useful function

In the more general Data Summation function, a variety of fields are available and may be selected and you may choose not to sum the “apples and oranges” totals for each field.

Data Summation

When the information on the Data Summation form is set up as desired, click the Continue button.

The program will begin the population count, and an information form will be displayed:

When the count is completed, the results will be displayed in Notepad:

The information includes he name of the selection layer, the range information (if applicable), and the count for the selected item(s).

The information is written to an ASCII file in the same folder as the selection layer. The file is written in a sub folder named “DATA SUMMATION”:

The file has the same name as the shapefile for the selection layer, with the TXT file extent.

You can save the file to a different name, or copy and paste the information into other documents, such as Microsoft Word.

If multiple coverage population counts are done using the same selection layer shapefile, the information will be appended to this file.

Search SoftWright Website