Should the isodistance be less than great circle distance?

Hi there,

If possible, I’d be very grateful for assistance with a quick query on the basis of openrouteservice isodistance calculation.

When I run an isodistance of (say) 100 km, I sometimes find that the isodistance boundary extends beyond a 100 km great circle distance of the start point. This seems a little counterintuitive, given that travelling 100 km by road, you would always expect to reach a point less than 100 km away “as the crow flies”.

Perhaps this is my misunderstanding (I am not a GIS specialist), and I would be grateful for any help with this.

Best regards,


Hey Pete,
can you give us a URL or api query string for the case in which you experience this?

Hi Hendrik,

Thanks very much for replying.

I’ve attempted to reproduce this at, but not managed to do so.

I therefore have to apologise that this therefore appears to be an issue with QGIS, which I used for the great circle distance measurement.

On this basis I think it’s safe to close/delete this query.

Sorry about this and thanks again.