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## Input data

A GMT program may or may not take input files. Three different types of input are recognized (more details can be found in Appendix B in the Technical Reference):

1.
  Data tables. These are ``spreadsheet'' tables with a fixed number of columns and unlimited number of rows. We distinguish between two groups:

  - ASCII (Preferred unless files are huge)

    -
      Single segment [Default]

    -
      Multi-segment with internal header records (-–M)

  - Binary (to speed up input/output)

    -
      Single segment [Default]

    -
      Multi-segment (segment headers are all NaN fields) (-–M)

2.
  Gridded dated sets. These are data matrices (evenly spaced in two coordinates) that come in two flavors:

  - Grid-line registration

  - Pixel registration

  You may choose among several file formats (even define your own format), but the GMT default is netCDF.

3.
  Color palette table (For imaging, color plots, and contour maps). We will discuss these later.

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