# 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

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 and scripting.

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.

Feature

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.

Feature

Convert Coordinate Notation

Converts a table containing point coordinate fields to a point feature class. The input table's coordinate fields can be in a variety of notations, such as GARS, UTM, and MGRS. The output point feature class also contains point coordinate fields in a coordinate notation of your choosing.

Feature

Projects spatial data from one coordinate system to another.

Raster

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.

Raster

Reorients the raster by flipping it, from left to right, along the vertical axis through the center of the raster.

Raster

Transforms the raster dataset from one projection to another.

Raster

Resizes a raster by the specified x and y scale factors.

Raster

Turns a raster dataset around the specified pivot point by the specified angle in degrees.

Raster

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.

Raster

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.

Tools in the Projections and Transformations toolset.

10/27/2014