Pitney Bowes MapInfo Vertical Mapper - Manual (Page 124)

Understanding Grid Queries
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Vertical Mapper 3.7
Understanding Grid Queries
You can use grid queries to build new grids from existing grids where the new grid values are
derived according to whether specific queries imposed on the existing grid files have been met.
For example, you can create an expression that will query a set of grid files and identify all
coincident cells that meet these conditions:
cells in Grid1 are >1049m AND
cells in Grid2 are <=$250,754.50 AND
cells in Grid3 are = “Dense Urban” OR
cells in Grid4 are = “Leeds County”.
Therefore, by examining each grid and “drilling down” through the four grid layers on a cell-by-cell
basis, a fifth grid can be built from the overlying and spatially coincident cells that identifies all the
cells that meet (or do not meet) all of the query conditions.
The power of grid-based spatial analysis lies in the ability to create a query, using
multiple themes of geographic information, that examines on a cell-by-cell basis each
layer of data and derives a new grid based on the query conditions.
There is no limit to the number of grids that can be used in a Vertical Mapper grid query expression.
However, there are restrictions on the specifications of grids that are used in a multiple grid query:
• All grids used in a grid query must be in the same coordinate system.
• All grids must be spatially coincident or at least partially overlap.
• If grids have different cell sizes, the query will be controlled by the grid with the smallest cell size.
The Grid Query tool is comparable to the MapInfo Professional SQL Select command although, in
the MapInfo Professional function, the new Query table preserves all of the original data records that
meet the SQL conditions. In the Grid Query tool, new cells are created in the derivative grid that are
assigned a user-defined value according to whether the cell did or did not meet the conditions of the
query expression. This is based on a simple true/false test: Does each cell in the new grid meet or
not meet all of the query conditions?