BED (Browser Extensible Data) format in bioinformatics provides a flexible way to define the data lines of genomic features that are displayed in an genome annotation track. BED lines have 3 required fields (chromosome, start position, end position) and 9 additional optional fields. For other bioinformatics formats, such as FASTA, FASTQ, VCF, GFF, BAM/SAM, etc, use their own separate tags.
BED format - Genome Browser FAQ
BED (Browser Extensible Data) format provides a flexible way to define the data lines that are displayed in an annotation track. BED lines have three required fields and nine additional optional fields. The number of fields per line must be consistent throughout any single set of data in an annotation track. The order of the optional fields is binding: lower-numbered fields must always be populated if higher-numbered fields are used.
BED information should not be mixed as explained above (BED3 should not be mixed with BED4), rather additional column information must be filled for consistency, for example with a "." in some circumstances, if the field content is to be empty. BED fields in custom tracks can be whitespace-delimited or tab-delimited. Only some variations of BED types, such as bedDetail, require a tab character delimitation for the detail columns.
The first three required BED fields are:
chrom - The name of the chromosome (e.g. chr3, chrY, chr2_random) or scaffold (e.g. scaffold10671).
chromStart - The starting position of the feature in the chromosome or scaffold. The first base in a chromosome is numbered 0.
chromEnd - The ending position of the feature in the chromosome or scaffold. The chromEnd base is not included in the display of the feature, however, the number in position format will be represented. For example, the first 100 bases of chromosome 1 are defined as chrom=1, chromStart=0, chromEnd=100, and span the bases numbered 0-99 in our software (not 0-100), but will represent the position notation chr1:1-100.
