How it was accomplished

The IHGSC used pair-end sequencing plus whole-genome shotgun mapping of large (~100 Kbp) plasmid clones and shotgun sequencing of smaller plasmid sub-clones plus a variety of other mapping data to orient and check the assembly of each human chromosome[7].
The Celera group tried “whole-genome shotgun” sequencing without using the additional mapping scaffolding[8], but by including shredded public data raised questions [15].