Pitney Bowes MapInfo Vertical Mapper - Manual (Page 22)

Understanding Spatial Estimation Techniques
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Vertical Mapper 3.7
Grid File Architecture
Every Vertical Mapper grid file (.grc or .grd) is divided into two sections. The first section, called the
file header, contains several pieces of information including the following:
• Map name
• Map size (number of cells in height and width)
• Cell size
• Coordinates of first cell
• Grid Projection
• Grid value description
The second section, the body of the grid file, contains the attribute data for every cell in the map.
MapInfo Tables
In MapInfo Professional, for every table, up to five different files are created (.tab, .map, .dat, .id, and
.ind). In Vertical Mapper, all the information is contained in either a .grc or a .grd file. A .tab file that
points to the .grc or .grd file is also created, enabling the grid file to be opened in MapInfo
Professional.
Grid Resolution
The resolution of a grid is based on the size of the cells. Vertical Mapper has square cells, so the
width and height are identical. The smaller the grid, the higher the resolution, and the more detailed
the information depicted. For example, what appears as a spike at 1000m resolution may be clearly
discernible as part of a mountain at 1m resolution.
Appropriate resolution depends on the application. For example, for data at the world level, 1 km
resolution is relatively high. For wireless planning, however, 1 km resolution is low, and 1m
resolution produces much more accurate results.
Understanding Spatial Estimation Techniques
In order to represent how data changes between known values, some type of estimation must be
made. There are several kinds of estimation technique that can be applied to a point file. These
techniques fall into two different categories: interpolation techniques and modeling techniques. They
approach the creation of a grid from entirely different perspectives, but both are mathematical
construction tools designed to build grids that assign values to grid nodes from a geographically
coincident point file.
Interpolation Techniques
These techniques are used to build grids that are an estimation of the same variable as the
underlying points. Each new grid cell has the same unit of measure as the point value.
Vertical Mapper currently supports six interpolation techniques:
• Triangulation with Smoothing (TIN)
• Inverse Distance Weighting (IDW)