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How To: Gather basic raster information

Summary

To solve many raster-related problems, some basic information is necessary. This article will explain what information to collect and how to find it.

Procedure

Most of the following information may be gathered from ArcCatalog. Right-click on a raster file in the Table of Contents, click Properties, then click the General and Spatial Reference tabs.

  1. Format:
    This is the file type used to store the raster. Different file types have different properties and requirements.
  2. Number of bands:
    This is the number of coincident layers in the raster. Rasters have at least one and could have up to seven or more.
  3. Data type:
    This is either signed integer, unsigned integer, or floating point. It pertains to the type of values stored in the raster. Integers are whole numbers, whereas floating points have decimals.
  4. Data depth (bits):
    The data depth, also known as bit depth, determines the possible range of values stored in each band. A depth of eight will store 2^8 = 256 values, while a depth of 16 will store 2^16 = 65536 values.
  5. Statistics:
    The Minimum value of the raster, Maximum value, Mean of all values, and Standard Deviation.
  6. Extents:
    Click the Spatial Reference tab; this is the Left, Right, Top, and Bottom of the raster. It defines the raster's georeferencing.
  7. Projection:
    This is the raster's coordinate system.
    Note:
    An <undefined> raster may not mean it is not projected. It could mean that it is just not defined yet. Check with the data's vendor to verify the raster's correct coordinate system.

  8. Size of the raster:
    This has two meanings.

    A) The number of rows and columns
    B) The amount of disk space taken up by the raster

    To find the amount of disk space taken up, open Windows Explorer, right-click on the raster file, click Properties, then look at both Size and Size on disk.
  9. Additional information:
    - Where did the raster come from?
    - What does the data represent?
    - What is the purpose of the data? What will it be used for?
    - Was there any special processing used to create the raster?
    - History of the raster. What has been done to it?

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