Pitney Bowes MapInfo Vertical Mapper - Manual (Page 76)

Creating Point Density Grids
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Vertical Mapper 3.7
Creating Point Density Grids
Calculate Point Density techniques are used to calculate the density of events in an area.
Vertical Mapper supports two techniques for calculating point density: Square Area and Kernel
Smoothing. These options are available from the Vertical Mapper, Create Grid, Point Density menu.
Point Density using Square Area
This method of calculating point density results in a grid where each cell value represents the
number of events within a user-defined area around the cell. For example, if the specified area is
one square kilometre, then each cell will have the number of events within one square kilometre
around the cell. Two methods of calculating or summing the number of events are provided. The first
method counts the number of symbol objects found within the user-defined area. This method
assumes that each symbol represents a single event. The second method is more sophisticated in
that it allows for a single symbol to represent more than one event. It does this by accessing a
column containing the number of events at each location in the database of the point file.
Exploring the Select Table and Column Dialog Box
This dialog box opens when you select either of the point density options. It enables you to select
the table to grid and choose the Count Points Only option or specify a column containing the data to
use.
The Select Table to Grid list displays a list of available tables.
The Select Event Sum Column list displays “Counts Points Only” and a list of available columns to
use; choose Count Points Only if you want only to count the points in the area; otherwise, choose
the name of the column containing the data to use.
The Enter Data Description box enables you to enter a description for the data.
The Unit Type list enables you to choose the unit type. If you choose the User Defined option, you
must specify the type in the User Defined Type box.
The Ignore Records Containing Zero check box when this check box is enabled, records
containing zero are ignored.