Introduction
The Flow Data Model Tools (FDMT) consist of several Visual Basic for Applications (VBA) macros designed to work in ArcGIS 9 ArcMap, with an ArcView, ArcEditor, or ArcInfo license.
They were created to perform two functions: integrate the functionality of Waldo Tobler's FlowMapper into ArcGIS, and allow import and export of data into the Flow Data Model. For information on FlowMapper, visit the FlowMapper website.
For information on the Flow Data Model, visit the Flow Data Model website.
Getting Started
To use the FMDT, double-click the file, flowtoolsv069m.mxd,
from ArcCatalog or Windows Explorer, or start ArcMap and open it.
In that map document, a new, custom button called Flow Data Model Tools is
added to the ArcMap Standard toolbar. Clicking the button, which is a right
triangle and two lines connecting three dots, opens the Flow Data Model
Tools dialog box. The left side of the dialog box is for importing
interaction and coordinate data and creating flow lines from them, while the
right side contains tools for interacting with the Flow Data Model.
To make the flow line drawing process better incorporate the Flow Data
Model, creating flow lines from input data is divided into three tasks that
are identified by the numbers 1, 2, and 3 on the left side of the dialog
box. The first, Import Interaction Table, uses text files to create a new
standalone table containing an input point identifier, an output point
identifier, and a magnitude value inside a geodatabase. The second step,
Create Points from Table, uses the table to create a point shapefile that
retains the points' identifier values. The third step, Create Flow Lines,
uses the point shapefile and the table to create net, gross, or two-way flow
lines in a new polyline shapefile (Figure 1).
Figure 1. Net, Gross, and Two-way Flow
The typical workflow for creating flow lines from input coordinates and an
interaction matrix would be to:
- preprocess the text data to ensure a space-delimited input file
- perform step 1
- add the output table to ArcMap
- perform step 2
- add the output point shapefile to ArcMap
- perform step 3
- add the output polyline shapefile
- modify the symbology of the derived polylines as desired
Tools
Preprocess:
Preprocessing may be needed to successfully import text files into the FDMT.
While the Import Interaction Table task requires files to be formatted in
the style of Flow Mapper, they must be delimited with a single space in the
FDMT. Since recent versions of Flow Mapper have allowed commas, tabs, and
multiples spaces to delineate text data, the Preprocess tool removes commas,
tables, and redundant spaces from otherwise well-formatted Flow Mapper
files.
New GDB:
This tool creates an empty geodatabase with the Flow Data Model schema for
cases with node-to-node flows.
Export:
This tool finds the tables in the ArcMap table of contents and creates a
table with from-to point identifiers and magnitudes. A portion of the Flow Data Model UML is displayed. Table and field names can be modified to match users’ existing data.
Import:
The Import tool uses a user-defined table and creates and populates the
relevant portions of a new Flow Data Model. The table requires an input
point identifier value, and output point identifier value, and a magnitude
value.
Help
The help includes this document. The "Online Help" button attempts to call the project's help website through Internet Explorer. From online help, users can navigate to to the Flow Data Model website for white papers, updates, and additional information.
A few guidelines and known issues
1) FDMT requires input files to be loaded in the ArcMap table of contents.
The exception is for interaction matrix and points text files.
2) When FDMT performs a function, it does not automatically add the output
to ArcMap.
3) The FDMT requires import text files to follow Tobler's Flow Mapper file
format.
4) The FDMT preprocessor may have difficulty with import text files
containing tabs.
5) The FDMT will not create directories. It will error or crash if a path
does not already exist.
6) The FDMT has been designed for two-dimensional data. The code must be
modified to use three-dimensional (z) values.
7) The FDMT currently works only with the node-to-node portions of the Flow
Data Model. Flows along known routes (as defined in the Flow Data Model UML)
have not yet been realized.
8) The FDMT requires "magnitude" to be a real, static value. Magnitude as a
method (as shown in the model's UML) is not yet supported.
J. Alan Glennon
NCGIA/Department of Geography
University of California
Santa Barbara, CA 93106
www.alanglennon.com
glennon@umail.ucsb.edu
page created/updated: 7 January 2005/7 January 2005
