An ethnic group is usually explained as a people who share a culture. Fredrik Barth turned that around in 1969: look at the boundary, he argued, not at the cultural stuff it encloses. Groups select a handful of markers out of everything available, put them to work at the edge, and keep the line intact while people, goods and marriages cross it constantly. Build a boundary here — tap markers to put them to work, tap mechanisms to hold them there, then load a real case and see how few markers a sharp line actually needs.
An undrawn line
┃ strands — markers in use▬ ties — mechanisms holding the line● drifting dots — people crossing: marriage, conversion, migration, passingThe two bars are a schematic of Barth’s argument, not a measurement.