One way of interpreting the service area of a communications system is to view a map showing signal levels and interference regions. Another measure of service area is to determine how many people reside in an area that receives a given field strength or C/I ratio. A count of population, households, and other types of demographic information can be done with a demographic study. Choose Studies>Demographic studies and a dialog box will appear where you can enter the relevant study information and start the study.

Analysis Source

The source study the comparison will be run against. Four choices are available from the drop-down list:

• The Area Study Selected for Status Bar. This uses the Area Study that is selected to show on the status bar (this option is set in the Area Studies window).

• A field strength contour (“.ctr”) file.

• A polygon (“.bna”) file such as those produced using the Draw menu (Chapter 5).

• An overlapping set of field strength contour (“.ctr”) files.

Choose area study selected for status bar if you want to do a study for the selected study map you have displayed. It can contain any of the Area study names so your demographic count can be relative to any of the Area study names.

Analysis level for study

The Upper/Lower bound selections will be grayed out unless area study selected for status bar was selected from the Analysis source drop-down list. Let’s assume you want to determine the number of people residing in an area covered by a particular signal level, C/I ratio, bit error rate, or who live in line-of-sight areas from your transmitters. With this section, you can specify the levels between which the count will be done. For example, if you wanted to count all the people who receive a signal power between 0 dBmW and -80 dBmW, you would enter 0.0 and –80.0 as the upper and lower bounds for the analysis levels on the second line. When you select the demographic study screen, the program will read the header on the Area Study (“.mxx”) file to determine the kind of data it contains and then, display the unit type for the analysis level entry that is consistent with the data in the file.

Contour/Polygon/Overlapping Contour Analysis Filename

This field will be grayed out if area study selected for status bar was selected from the Analysis source drop-down list. Field strength contour files are produced when the study map display type is set to FCC type contours. You can count the population of other quantities inside such contours by choosing contour file as the Analysis source. When you make this selection you must enter the name of the valid “.ctr” file for which you want to do a count. If the file contains data for multiple contours, a prompt will appear after you initiate the study asking you for the contour level you wish to count.

For general demographic analysis inside an arbitrary area, you can draw a polygon around the area and save it to a file as described in Polygon/Polyline/Service Area Boundary. In the Demographic Study dialog box, change the source to polygon file and then enter the name of the (“.bna” file on the line that requests the file name.

The fourth study source is called overlapping contour file. The file that you specify here has a special format shown in Appendix I. For some circumstances, notably broadcast applications in the United States, it is necessary to know the population inside a set of overlapping contours, or put another way, the number of people who receive signals from a number of broadcast stations. The demographic count is done in an area that represents the union of areas covered by the contours in the files listed in the overlapping contour file described in Appendix I.

Regardless of which of the four source types you use, a demographic count consists of searching through a list of geographically defined points or centroids each of which has a number of data values or attributes associated with it. These attributes can be population numbers like number of people, number of people over 18 years of age, number of housing units, etc., or they can be other types of data such as cellular radio traffic call density, miles of roadway or really anything that can be geographically quantified. The detailed attribute data for every centroid in the analysis area is saved in a file called “census.tmp”. This file is an ASCII file which you may find useful for other analyses.

Use Polygon Filter on Count

By selecting the Use polygon filter on count checkbox, the input box on this screen lets you specify a polygon filter filename. A filter file is another way to qualify the demographic count. To be included in a count, a centroid must fall within the source qualification (inside a contour or polygon, for example) and inside the filter polygon. A typical way to use the filter polygon is to describe a county boundary. By using this selection, you could count the number of people who receive a given signal level and are inside the county. This polygon filter file has exactly the same format as any polygon file and can therefore be created with draw polygon function from the draw menu.

Start Study/Display Areas

Once you have set all the demographic study parameters the way you want them, select Start Study and the count will begin. An appropriate message will be displayed during this time. When the count is finished a new screen will appear with the complete tabulated breakdown of the count by attribute. The information found in this screen is saved to a file called Census_Count.txt found in the \Reports\folder of your project. You can also view this file by using Utilities>Reports.

The screen will display the demographic count results for the source data you have selected. If you are using the EDX 1990, 2000 or 2010 U.S. Census database, you also have the option of making a detailed file with the results of your count. To do this, first enter the name of the file where you want the detailed results to be saved, then click on the Make Detailed File button. The program will process the count data saved in the census.tmp file and calculate a breakdown by city, county and state, for both the total population and the population 18 years and older, of the results of your count.

Once the detailed breakdown information is written to the file you named, the program will automatically open a text editor and display the contents of the file. You can view the data, print it, and save it to another file name if desired. Once you have finished, exit the editor and you will be returned to your current map screen in the EDX software.

Clicking the Display Areas button will give you a calculation of the area inside a given signal level (for the current study grid), inside a contour for a contour file, or inside a polygon for a polygon file. A small screen will appear with the area results.