All - Why can the calculated mileage vary slightly from one week to the next?

Caution, this article applies exclusively to users whose organization has activated the Expense reimbursements module.

Scolago automatically calculates travel distances using Google's mapping service (Google Routes API). This service determines the most efficient driving route between two addresses, taking into account the road network and traffic conditions.

Google continuously updates the data that feeds its algorithm: changes to the road network, road construction or closures, updates to average traffic conditions, adjustments to its route-calculation algorithm, or modifications to calculation results. Because of these updates, the same route may show a slightly different distance from one week to the next, even if nothing has changed on Scolago's end.

A slight variation in mileage from one week to the next, for the same route, is normal and expected. It results from regular updates made by Google to its mapping service, not from a calculation error on Scolago's part.

To limit how often calls are made to Google and to avoid unnecessary recalculations, a route's distance is stored in cache for 24 hours before being revalidated.

We looked into the possibility of extending this caching period to further reduce these variations. This option was ultimately ruled out: a longer caching period would risk locking in exceptional, temporary data (road construction, a one-off service glitch returning a distance of zero or an incorrect value) with no way to correct it quickly. Even with an extended cache, a discrepancy would still be possible whenever Google adjusts its algorithm or road data.