Off topic:How To Interpret contig field Fields In Vcf Files From 1000 Genomes?

Question

[2012secondseason]

Hello.

There are 3 contigs about chromosome 1 in a 1000 genome indels vcf file.(1000G_phase1.indels.hg19.vcf)

contig=<id=chr1,length=249250621,assembly=hg19>

contig=<id=chr1_gl000191_random,length=106433,assembly=hg19>

contig=<id=chr1_gl000192_random,length=547496,assembly=hg19>

I dont understand what 'assembly' exactly means. In fact, I don't fully understand how breakpoint are assembled.

contig, breakpoint, indel, assembly. How they are related?? :( If you explain it with picture I would be so grateful. (Any answer would be helpful.)