What is a grid, The gridding process, Grid types – Pitney Bowes MapInfo Vertical Mapper User Manual
Page 20: What is a grid? the gridding process grid types
Understanding Grids
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Vertical Mapper 3.7
What is a Grid?
A grid is made up of regularly spaced square cells arranged over a given area. Each cell has a node,
which is a point located at its centre. Each cell can be given a value and a colour representing the
value. If there are several cells between two known locations, such as two contour lines, the change
in colour indicates how the values change between the locations.
The Gridding Process
Typically, the gridding process begins by overlaying an array of grid nodes over the original point
file. This can be visualized as a regularly spaced point file arranged in the form of a grid (next figure).
Each grid node is then attributed with an estimated value based upon the values of the surrounding
points. The grid is then displayed in a Map window. The display takes the form of a raster image,
where the colours reflect the estimated node values. It is because of this display component that
grid-based GIS systems are called raster GIS.
The gridding process begins by creating an array of grid nodes geographically
coincident to the sample file. Each grid node is attributed with an estimated value that
is displayed as a raster image in a Map window.
Grid Types
Vertical Mapper supports two types of grids: numeric grids, which have numeric attribute
information, and classified grids, which have character attribute information.
Numeric Grids
The most illustrative example of a numeric grid is a digital terrain model where each grid cell is
referenced to a value measured in units of distance above sea level (next figure). Numeric grids are
best used to define continuously varying surfaces of information, such as elevation, in which grid cell
values are either mathematically estimated from a table of point observations or assigned real
numeric values. For example, in the next figure, each grid cell was calculated (interpolated) from a
table of recorded elevation points. In Vertical Mapper, numeric grid files are given the extension .grd.