# **Impedance warning**

*network-functions Impedance warning*

## memory and disk issues

The od variants of the Impedance functions result in a domain-unit that is a subset of the cartesian product of the origin and destination domain units, further: the set of od-pairs.

Be aware that this subset could be very large, causing memory and disk issues. Be aware of the cardinality of the resulting domain unit when the result specification includes attributes of the set of od-pairs.

For full symmetric od matrices, keep the number of elements of the origin/destination domain units limited (we do have experience with domains of more than 10.000 elements, but calculation time and memory usage for the results increase with the number of od-pairs), use filters to cut the route search, or consider asymmetric variants with a lower number of origin zones. One could also try to avoid storing od-pair related attributes by using the results from available aggregations per origin and/or destination that can be updated during the processing of all destinations for each origin. See also https://github.com/ObjectVision/GeoDMS/issues/514