This track shows the sequences used in the 09 Feb 2018 Homo sapiens/GCA_002077035.3_NA12878_prelim_3.0 genome assembly.
Genome assembly procedures are covered in the NCBI
NCBI also provides specific information about this assembly.
The definition of the gaps in this assembly is from the AGP file:
The NCBI document AGP Specification describes the format of the AGP file.
In dense mode, this track depicts the contigs that make up the currently viewed scaffold. Contig boundaries are distinguished by the use of alternating gold and brown coloration. Where gaps exist between contigs, spaces are shown between the gold and brown blocks. The relative order and orientation of the contigs within a scaffold is always known; therefore, a line is drawn in the graphical display to bridge the blocks.
This assembly has 3,663 component parts, with the following principal types of parts: