Should the isodistance be less than great circle distance?

openrouteservice isochrones
1

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,

Pete

2

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

3

Hi Hendrik,

Thanks very much for replying.

I’ve attempted to reproduce this at https://maps.openrouteservice.org/, 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.