Overview of three common tabular formats. A) Generic Feature Format (GFF). The example file is a reduced version of the main example of the GFF version 3 specification . B) Browser Extensible Data format (BED). The example file is fetched from the specification of the format at UCSC . C) Wiggle Track Format (WIG) . The example files show the two subformats variableStep and fixedStep. The track elements in the variableStep file covers single base pairs (span = 1, as default) and contains sparse data. For the fixedStep file, the step attribute is equal to the span attribute. The fixedStep file thus contains dense data. Figure 4 shows GTrack conversions of these example files.