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Tool Population Density Metrics

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donebert edited this page Aug 16, 2022 · 11 revisions

Population Density Metrics

Summary

Calculates population count and density (people per km²) for each reporting unit polygon and creates an output table.

In addition to the default metrics, the tool optionally calculates population change over time.

Usage

  • This tool processes all polygons in the Reporting unit feature regardless of selections set. The ability to limit land cover calculations to only selected reporting unit polygons is not supported in this release.

  • NOTE: To ensure desired results, the Reporting unit feature, Census feature, and Census T2 feature must be in projected coordinate systems with linear units of measure.

  • The Reporting unit feature must be a polygon feature class or shapefile.

  • This tool assumes that population is distributed evenly throughout each Census feature polygon. The tool apportions population by area weighting. For example, if 50% of a Census feature polygon is within a reporting unit, the tool will assign 50% of the value in the polygon's Population field to that reporting unit. Caution should be exercised when Census feature polygons do not have even population distributions as this could result in an overweighting or underweighting of population when the tool performs the apportionment. Generally, greater accuracy will be achieved if the Census feature polygons are smaller than the smallest Reporting unit feature polygons.

  • When the optional POPCHG (population change) is checked, the tool allows the user to select a Census T2 feature and a corresponding Population T2 field.

    • For best results, the Census T2 feature should contain polygons at a similar scale to that of the Census feature (e.g. if Census feature represents census block groups, then Census T2 feature should also represent census block groups rather than census tracts or some other census geography).
    • Census T2 feature may be the same feature layer as used for Census feature.

  • Final output is written to the location specified in the Output table parameter. The Output table may be saved as a File Geodatabase Table, a dBASE Table, or an INFO Table.

    • NOTE: For most consistent results, it is highly recommended that tool output be saved to a file geodatabase.
    • When saving as a File Geodatabase Table, no extension is necessary for the Output table name. The output location must be a file geodatabase.
    • When saving as a dBASE Table, include the .dbf extension in the Output table name. dBASE tables may not be saved in a file geodatabase.
    • When saving as an INFO Table, no extension is necessary for the Output table name. INFO tables may not be saved in a file geodatabase. A new directory in the output directory called "info" is automatically created in which the INFO tables are stored. INFO tables have limited portability, so it is recommended that output not be saved as an INFO Table if data sharing is important.

  • The user may elect to Retain Intermediate Layers Generated During Metric Processing.

    • Choosing to Retain Intermediate Layers saves the intermediate products to one of the following locations:
      • When output is saved as a File Geodatabase Table, intermediate products are placed in the same file geodatabase.
      • When ouput is saved as a dBASE Table or an INFO Table, a file geodatabase named "attilaScratchWorkspace" is automatically generated in the same output location specified for the Output table. Intermediate products are placed in the attilaScratchWorkspace file geodatabase.

  • Field names in the Output table follow this naming scheme:

    • For default tool settings (e.g. no optional settings selected):
      • AREAKM2 - The area of the reporting unit in km².
      • popCount (ALIAS: SUM_intPop) - The estimated total population within the reporting unit derived by area weighting the population values within each Census feature polygon that intersects with the reporting unit and summing the area-weighted values.
      • POPDENS - The estimated population density in persons per km² within the reporting unit derived by dividing popCount by AREAKM2.
    • When the POPCHG option is selected:
      • popCount_1 (ALIAS: SUM_intPop) - The estimated total population within the reporting unit derived by area weighting the population values within each Census feature polygon (Time 1) that intersects with the reporting unit and summing the area-weighted values.
      • POPDENS_1 - The estimated population density in persons per km² within the reporting unit derived by dividing popCount_1 by AREAKM2.
      • popCount_2 (ALIAS: SUM_intPop) - The estimated total population within the reporting unit derived by area weighting the population values within each Census T2 feature polygon (Time 2) that intersects with the reporting unit and summing the area-weighted values.
      • POPDENS_2 - The estimated population density in persons per km² within the reporting unit derived by dividing popCount_2 by AREAKM2.
      • POPCHG - The estimate percent change in population from Time 1 to Time 2.

Syntax

PDM (Reporting_unit_feature, Reporting_unit_ID_field, Census_feature, Population_field, Output_table, {POPCHG}, Census_T2_feature, Population_T2_field, {Select_options})

Parameter Explanation Data Type
Reporting_unit_feature The vector polygon dataset that defines the reporting units. Feature Layer
Reporting_unit_ID_field The field in the Reporting unit feature layer that contains the unique ID for each reporting unit.

It may be an integer or a string data type.		 Field
Census_feature The vector polygon dataset that contains population data. Feature Layer
Population_field The field in the Census feature layer that contains population data. Field
Output_table The output reporting unit metrics table to be created.

It is recommended that the Output table be saved within a file geodatabase.		 Table
POPCHG (optional) Specifies whether population change over time (POPCHG) metrics will be included in the output table.

  • false - No POPCHG metrics will not be included. This is the default.
  • true - POPCHG metrics will be included.
 Boolean
Census_T2_feature The optional vector polygon dataset (Census time 2) that contains population data for the comparison date.

It may be the same feature layer as Census feature.		 Feature Layer
Population_T2_field The field in the Census feature layer that contains population data for the comparison date. Field
Select_options (optional) One tool option is available to provide additional information:

  • Retain Intermediate Layers Generated During Metric Calculation - Saves the intermediate table and/or raster that is normally deleted after processing is complete.
 Multiple Value

Intermediate Files

  • pdm_[Reporting unit feature]* vector - A polygon feature class containing reporting units with a new area field in km². The name of the intermediate feature class has the prefix "pdm_" followed by a the name of the Reporting unit feature, then followed by a number (e.g. pdm_WI_Counties0, pdm_HUC120, pdm_HUC121, etc.). The number is appended when the feature class is saved in order to give each successive feature class a unique name when the tool is executed more than once and the results saved to the same output location.
  • pdm_[Census feature]* vector - A polygon feature class of all census polygons with fields containing population, polygon area, and population density within the census polygons. The name of the intermediate feature class has the prefix "pdm_" followed by the name of the Census feature, then followed by a number (e.g. pdm_AK_2000_tracts0, pdm_census20100, pdm_census 2010_10, etc.). The number suffix is added when the feature class is saved in order to give each successive feature class a unique name when the tool is executed more than once and the results saved to the same output location.
  • pdm_intersectOutput* vector - A polygon feature class with Census features intersected with reporting units. The name of the intermediate feature class has the prefix "pdm_intersectOutput" followed by a number (e.g. pdm_intersectOutput0, pdm_intersectOutput_10, pdm_intersectOutput_20, etc.). The number suffix is added when the feature class is saved in order to give each successive feature class a unique name when the tool is executed more than once and the results saved to the same output location.
  • pdm_summaryTable* table - A table of the number of intersected Census feature polygons and the sums of the area-weighted population counts within each reporting unit. The name of the intermediate table has the prefix "pdm_summaryTable" followed by a number (e.g. pdm_summaryTable0, pdm_summaryTable_10, pdm_summaryTable_20, etc.). The number suffix is added when the table is saved in order to give each successive table a unique name when the tool is executed more than once and results saved to the same output location.

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