rings table

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Table ring contains data on id of pairs of origin-destiantion points and number of ring which the second point from pair is placed in (in relation to the first point).

Table ring is created by create_ring.sql script and is written by the insert_ring_uniform.sql and insert_ring_weighted.sql scripts used in the intervening_opportunity python script by build_uniform_rings and build_weighted_rings functions.

Both insert_ring_uniform.sql and insert_ring_weighted.sql scripts use tables point and distance to write ring table. od start id and od end id values are taken from table point. Ring number is calculated using weight of distance between these points taken from distance table and factor calculated in the intervening_opportunity python scipt (factor value is dependent on type of created rings).

od_start_id	od_end_id	ring