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There are 3 basic steps to contouring by microcomputer: control-point data analysis, generating a regular grid of estimated values, and contouring. Because each of these steps requires a significant amount of time and computer resource, techniques have been developed to improve grid parameter selection, speed gridding, and edit computer-generated contour maps. Grid cell size is a critical parameter used during the gridding stage of computer mapping and must be selected with consideration given to control-point distribution. A histogram showing control points per grid cell is a simple graphical presentation that illustrates before gridding is actually performed the effectiveness of the selected grid increment in producing the desirable grid characteristics of having one co trol point per grid cell. Gridding is accomplished in 2 steps at every node: gathering the control points for estimating, and actual calculation. Using collection and estimating techniques such as nearest-neighbor searches and inverse-distance moving weighted averaging, several thousand nodes can be calculated in a few minutes. Often, the generated grid (contour map) is satisfactory with exceptions in 1 or 2 areas. Using an interactive computer technique known as contour editing, geologic knowledge and experience can be infused into the map. When editing contour, the computer mapper indicates the way the contours should behave. The entered values are then used to calculate back to the grid nodes (without regridding the whole map area) so that when the grid is recontoured, the contours mi ic the contour revisions.
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