NAME:  Identify Features Within Distance, v. 1.b   (Click Name to Download)

AKA:  id_within_dist.avx

Last Modified:  August 3, 2003

TOPICS:  ArcView 3.x, Nearest Feature, Distance, Bearing, Azimuth, View, Analysis, Tools, Centroid, Closest Edge, Adjacent, Range

AUTHOR:  Jeff Jenness

Wildlife Biologist, GIS Analyst

US Forest Service, Rocky Mountain Research Station

2500 S. Pine Knoll Drive

Flagstaff, AZ 86001

jeffj@jennessent.com 

Several Measurement Choices:  You have the option to identify features based on a variety of distance choices:

Furthermore, for each of these three options, you have more options regarding the relationship the feature has to the distance:

These options are described in more detail in Step 5 of the manual.

Identify Features Within a Single Theme:  You can select a single theme to act as both the Input theme AND Comparison theme, in which case this script will identify all other features in that theme that lie within your specified distance.  It will NOT measure the distance to itself, so you'll never get a feature identified with itself within your specified distance.

All or Only Selected Records:  You can either use all the features in each of the themes for the analysis or only a selected subset of features.  If any features in a particular theme (input or comparison themes) are selected, then only those selected features in that theme will be used in the analysis.  If no features in a theme are selected, then all features in that theme will be used in the analysis.

Projected vs. Unprojected Views:  If your original data are in Lat/Long coordinates (the Geographic Projection) and your View has been projected, then this extension will identify features based on the Map Units of your view projection.

REQUIRES:  This extension requires a minimum of one feature theme (Point, Line or Polygon theme) present in a view if you want to identify features within a single theme.  Otherwise, a minimum of two feature themes are needed; one to act as the 'Input' theme and at least one 'Comparison' theme.

This extension also requires that the file "avdlog.dll" be present in the ArcView/BIN32 directory (or $AVBIN/avdlog.dll) and that the Dialog Designer extension be available in the ArcView/ext32 directory,  which they almost certainly are if you're running AV3.1 or higher.  You don't have to load Dialog Designer to run the extension; it only has to be available.

UPDATES:  August 30, 2002 - The Version 1a update fixes a bug that produces an “Error in reading shape record length for record 1” error message.

August 3, 2003 - The Version 1b update makes some minor aesthetic changes.

GENERAL INSTRUCTIONS:

1)  Begin by placing the "id_within_dist.avx" file into the ArcView extensions directory (../../Av_gis30/Arcview/ext32/).

2)  After starting ArcView, Load the extension by clicking on File --> Extensions… , scrolling down through the list of available extensions, and then clicking on the checkbox next to the extension called "Identify Features Within Distance"

3)  Select Input Theme:  Begin by clicking on the icon. This brings up the Input Theme dialog box:

The – INPUT THEME – list shows all of the Feature Themes (those themes made of Points, Lines or Polygons) in the view.  Once you select the input theme of interest, the –ID FIELD – list becomes active and shows a list of all the fields in the input theme’s Feature Attribute Table.  You must select a field that contains a unique identifier for each feature.  This identifier allows your RESULTS table to be joined with your input theme Feature Table, and it also necessary for you to know which input feature is being referred to in the RESULTS table.

4)  Select Comparison Themes and ID Fields:   After you have selected your Input Theme, select either a single or multiple Comparison Themes.  This dialog box works the same as the Input Theme dialog box except that you can add multiple Theme/ID Field combinations to the analysis.  Notice that you can also include the Input Theme as a comparison theme.  In this case, the program will check the distances to all features within that Input Theme EXCEPT itself (the closest feature to any feature will always be itself, but that information is rarely what users are looking for).

5)  Select the Distance or Distance Range:  After you have selected your comparison themes, you will see the following dialog box prompting you to specify the analysis you would like to conduct.

There are a number of ways you can identify features based on a specified distance, and this extension attempts to provide you with the most likely methods you will need.  IMPORTANT:  All these methods use either the "<" or the ">" operation, rather than the "<=" or ">=" operations.  They will never include the feature if the distance is Equal to your specified distance.  Also, all distances should be in Map Units, which are the units of the X/Y Coordinate system you are using, and which are the units of the X/Y Coordinates you see in the top right of your screen, right next to your Scale textbox.

You have three broad options regarding which part of the shape you're interested in (the closest edge, the entire shape, or any part of the shape), and each broad option has three sub-options related to your specified distance.

1. Identify Features by the location of the Nearest Edge: 

   1. Identify Features where the nearest edge is Less Than ____ map units:  This option will identify all comparison features whose closest edge is less than a maximum distance that you specify.  Part of the identified line or polygon may lie outside of your maximum range in this case.  This option can also be used to identify adjacent features by specifying a very small Distance value.

   2. Identify Features where the nearest edge is Greater Than ____ map units:  This option will identify all comparison features where the closest edge is farther away than a minimum distance that you specify.

   3. Identify Features where the nearest edge lies within the range ____ to ____ map units:  This option will identify all comparison features where the closest edge lies within a specified range.  Part of the identified line or polygon may lie outside of your maximum distance in this case.

2. Identify Features by the location of Any Part of the shape:

   1. Identify Features if Any Part of the shape is Less Than ____ map units:  This option will identify all comparison features in which any part of the shape lies within a maximum distance that you specify.  Part of the identified shape may lie outside of your maximum distance in this case.  This option gives identical results to the "Identify Features if the nearest edge is Less Than ___ map units" option described above.

   2. Identify Features if Any Part of the shape is Greater Than ____ map units:  This option will identify all comparison features in which any part of the shape lies outside of a minimum distance that you specify.  Part of the identified shape may lie inside of your minimum distance in this case.

   3. Identify Features if Any Part of the shape lies within the range ____ to ____ map units:  This option will identify all comparison features in which any part of the shape lies within a minimum and maximum distance that you specify.  Part of the identified shape may lie outside of your specified range in this case.

3. Identify Features by the location of the Entire Shape:

   1. Identify Features where the entire shape is Less Than ____ map units:  This option will identify all comparison features in which the entire shape lies within a maximum distance that you specify.  No part of the identified shape will lie outside of your maximum distance in this case.

   2. Identify Features where the entire shape is Greater Than ____ map units:  This option will identify all comparison features in which the entire shape lies outside of a minimum distance that you specify.  No part of the identified shape will lie inside of your minimum distance in this case.  This option gives identical results to the "Identify Features if the nearest edge is Greater Than ___ map units" option described above.

   3. Identify Features where the entire shape lies within the range ____ to ____ map units:  This option will identify all comparison features in which the entire shape lies within a minimum and maximum distance that you specify.  No part of the identified shape will lie outside of your specified range in this case.

6)  Select which Output Tables to Create and which Fields to include:  You have the option to calculate two different RESULTS tables, and you have the choice between a number of data fields to include.

RESULT Table #1:  Identify each Input Feature:  This RESULT table has a record for each Input feature that identifies it and gives a count of the number of Comparison features that were within the distance.  You have the option to automatically join this table to your Input Feature Attribute Table if you like.  This join can always be removed by hitting the "Remove All Joins" option in the ArcView Table Menu.  The two fields are: