# Gridding Overview

A grid, also known as a raster in other software products, is a rectangular region comprised of evenly spaced rows and columns. The intersection of a row and column is called a grid node. Rows contain grid nodes with the same Y coordinate. Columns contain grid nodes with the same X coordinate. Contour, color relief, grid values, peaks and depressions, vector, viewshed, watershed, 3D surface, 3D wireframe map layers all require grids in Surfer.

## What is Gridding?

Gridding is the process of taking irregularly or regularly spaced XYZ data and generating
a regularly spaced grid of Z values at each grid node by interpolating
or extrapolating the data values. In addition to gridding data, Surfer can also use a variety of
other grid files directly. For a list of these, refer to the **File Format Chart**
in the online *Help*.

## Gridding Methods

Gridding the data produces a regularly spaced, rectangular array of grid nodes, with a calculated Z value at each node, from regularly or irregularly spaced XYZ data. The term "irregularly spaced" means that the distance between data points varies in the X or Y direction, or both. Irregularly spaced data often has many holes where data are missing. Gridding calculates the Z values for grid nodes where data exists, and can also calculate the Z values for grid nodes in the holes where no data exists, by extrapolating or interpolating the Z values in the data. The gridding method determines the mathematical algorithms used to compute the Z value at each grid node. Each method results in a different representation of your data. It is advantageous to test each method with a typical data set to determine the gridding method that provides you with the most satisfying interpretation of your data.

When your XYZ data is regularly spaced, meaning the distance between data points does not change in the X and Y directions, you may produce a grid file that uses the Z values directly and does not interpolate values for the grid nodes. See the *Producing a grid file from a regular array of XYZ data* help topic for more information.

## General Gridding Options

Each gridding method has its own set of gridding options. Some of the options are the same or similar for the different gridding methods, while other options are specific to particular gridding methods. Some options that are available to multiple gridding methods include: *Search*, *Anisotropy*, *Breaklines*, and *Faults*.

## See Also

Introduction to Gridding Methods