An overview of the Projections and Transformations toolset

This toolset contains tools to convert geographic data from one map projection to another. There are additional tools for transforming raster datasets, such as shift, rescale, and rotate.

When you obtain GIS data, it often needs to be transformed or projected. Since the data you receive is not always preprocessed, you will often need to place coordinates to your raster image. The transformation tools in the Projections and Transformations toolset can be used to rectify these issues. Whether you treat the earth as a sphere or a spheroid, you must transform its three-dimensional surface to create a flat map sheet. This mathematical transformation is commonly referred to as a map projection.

To understand how transformations work, you must keep in mind that all places on the earth have a location, and spatial data corresponds to one of these locations. Imagery and raster data that are not preprocessed—meaning that they come straight from the sensor or scanner—will usually not have any of these coordinates or locations inherent. The transformation tools are responsible for warping the image to the proper location and changing the image to the proper orientation.

Altering spatial properties using map projections can be described as shining a light through the earth onto a surface called the projection surface. Imagine that the earth's surface is clear, with the graticule drawn on it. Wrap a piece of paper around the earth. A light at the center of the earth will cast the shadows of the graticule onto the piece of paper. You can now unwrap the paper and lay it flat. The shape of the graticule on the flat paper is very different from what it was on the earth because the map projection has distorted the graticule.

A spheroid can't be flattened to a plane any more easily than a piece of orange peel can be flattened; it will rip. Representing the earth's surface in two dimensions causes distortion in the shape, area, distance, or direction of the data. A map projection uses mathematical formulas to relate spherical coordinates on the globe to flat, planar coordinates.

Different projections cause different types of distortions. Some projections are designed to minimize the distortion of one or two of the data's characteristics. A projection could maintain the area of a feature but alter its shape.

Toolset	Tool	Description
	Batch Project	Changes the coordinate system of a set of input feature classes or feature datasets to a common coordinate system. To change the coordinate system of a single feature class or dataset use the Project tool.
	Convert Coordinate Notation	Converts coordinate notations contained on one or two fields from one notation format to another.
	Create Custom Geographic Transformation	Creates a transformation method for converting data between two geographic coordinate systems or datums. The output of this tool can be used as a transformation method for any tool with a parameter that requires a geographic transformation.
	Create Spatial Reference	Creates a spatial reference object for use in ModelBuilder.
	Define Projection	This tool overwrites the coordinate system information (map projection and datum) stored with a dataset. The only use for this tool is for datsets that have an unknown or incorrect coordinate system defined.
	Project	Projects spatial data from one coordinate system to another.
Raster	Flip	Reorients the raster by turning it over, from top to bottom, along the horizontal axis through the center of the raster. This may be useful to correct raster datasets that are upside down.
	Mirror	Reorients the raster by flipping it, from left to right, along the vertical axis through the center of the raster.
	Project Raster	Transforms the raster dataset from one projection to another.
	Register Raster	This tool registers an image by automatically computing control points based on a reference image, or by using a set of predefined control points. The geometric transformation computed from the control points is written to the input dataset. If the input dataset is a mosaic dataset, the tool will operate on each mosaic dataset item.
	Rescale	Resizes a raster by the specified x and y scale factors.
	Rotate	Turns a raster dataset around the specified pivot point by the specified angle in degrees.
	Shift	Moves (slides) the raster to a new geographic location, based on x and y shift values. This tool is helpful if your raster dataset needs to be shifted to align with another data file.
	Warp	Performs a transformation on the raster based on the source and target control points using a polynomial transformation. This is similar to georeferencing using a text file.
	Warp From File	Performs a transformation on the raster based on a link file, using a polynomial transformation. The link file contains the source and target control points.

Tools in the Projections and Transformations toolset.