Pitney Bowes MapInfo Vertical Mapper - Manual (Page 63)

Chapter 4: Creating Grids Using Spatial Models
User Guide
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The Decay Curves check box enables you to control the application of decay functions to the
weighting values attached to each point location. If you don’t choose a weighting column in the
Select Table and Column dialog box, the decay curves Settings button is disabled. If a weighting
column is chosen in the dialog box, you can choose to disable the decay functions by clearing the
Decay Curves check box.
The Distance Setting section enables you to define how distances are measured, in map units,
between each grid cell and the point locations. One of two techniques can be set in the Location
Profiler model.
• Crow Fly (Straight Line) method measures the distance between the grid cell and the point using
a straight line path.
• Manhattan (Orthogonal) method measures the distance between the grid cell and the point
location using the x and y difference between the two sites, that is, it combines the total x-axis
and y-axis distance that must be covered to reach a destination. For Latitude/Longitude data the
distance is measured first travelling north-south then east-west. This option is provided to
approximate distances when travelling on road networks that are oriented in a square grid
pattern.
The File name box enables you to enter a new file name.
The Extents button displays a summary of the geographic size, the z-value range of the point
database, and the data units.
Exploring the Location Profile Decay Curves Dialog Box
Distance decay should be applied only when it is assumed that data points lying close to the grid cell
are more relevant than those lying farther away. In other words, as the distance from the grid node to
the data points approaches the search radius, the relative contribution of these points to the distance
averaging calculation should approach zero. A decay value of one (100 percent contribution) is
defined for data points close to the grid node, falling to zero (zero percent contribution) for data
points at a distance right at the search radius from the grid node. Decay functions can also be
applied to the exclusion zone. Using the same model, the decay value is zero for points at the grid
node (zero percent contribution) and increases to one for data points at a distance close to that of
the exclusion radius (100 percent contribution).