This function computes the commuting areas from a flow data. It is especially effective for calculating the travel to work area (TTWA). TTWA are defined to reflect areas where the bulk of the resident population also works within the same area. TTWA defines local labour market area. The ttwa function uses a greedy algorithm. Progressively, areas aggregate themselves with their link when above a threshold. The ttwa is an adaptation of the algorithm used by the INSEE zoning, Anabel.
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