genomic-coordinates

# Genomic Coordinates ## When to use Any time a coordinate crosses a boundary: between two file formats, between two tools, between two assemblies, or between the genome and a transcript. ## The rule **A coordinate is three facts, not one: the number, the convention it is written in, and the assembly it was measured against.** Carry all three or the number is not interpretable. Coordinate errors are the quietest class of bug in genomics. An off-by-one BED file parses, sorts, and intersects without complaint. A GRCh37 VCF joined against a GRCh38 annotation returns rows. A right-shifted indel simply fails to match its entry in ClinVar, and the result is a variant reported as novel. Nothing raises an error; the answer is just wrong, and it is wrong in a direction that looks plausible. So: convert with the table, not from memory, and verify against the reference whenever a reference is available. ## The two conversions ``` 1-based inclusive -> 0-based half-open : start - 1, end 0-based half-open -> 1-based inclusive : start + 1, end ``` The end coordinate never moves. If a conversion changed both numbers, it is wrong. ## Which format is which | 0-based, half-open | 1-based, inclusive | | --- | --- | | BED, bedGraph, bigWig, narrowPeak | GFF3, GTF, VCF | | BAM/CRAM (binary POS) | SAM (text POS) | | PSL, genePred, refFlat | WIG, Picard interval_list | | MAF (UCSC multiple alignment) | MAF (TCGA mutation annotation) | | PyRanges, pybedtools | GRanges/IRanges, samt...