In the UCSC Genome Browser, a composite track is a grouping for a set of similar-type annotation tracks (e.g., all tracks store continuous bigWig data, or all tracks store data in the genePred format). A set of tracks within a composite track are referred to as "sub-tracks." Some of the natively-hosted annotation tracks within the UCSC Genome Browser are composite tracks. For example, the ALL GENCODE GRCh38/hg38 composite track is a group containing a set of GENCODE sub-tracks, where each track can have custom settings (such as different display modes per sub-track).
In addition to the composite tracks hosted within the UCSC Genome Browser, track hubs also provide support for hub-based composite tracks. Creating a track hub is one of several ways to host your own customized data sets, which can be viewed within the UCSC Genome Browser environment (including the utilization of major tools such as the Table Browser).
The Composite Builder is a tool which provides a quick and easy way to build a custom composite track, without having to build a track hub. From a single interface, tracks that are being viewed in the UCSC Genome Browser display can be added into a new composite track group. Composite groups can then be customized with a suite of options (e.g., choosing colors for each sub-track, naming tracks, etc.). Your newly created composite group can then be viewed in the UCSC Genome Browser in reference to the particular genome assembly from which the custom composite was built.
The following section is a guide for getting started with the Composite Builder tool. By following the steps provided in the example below, you'll be able to create your own composite track, customize it, and view it with the UCSC Genome Browser.
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