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## 1.2.1 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 the architecture-indenpendent netCDF format.

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

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