# Isochrones with the option "avoid polygone" are larger than without

**URL:** <https://ask.openrouteservice.org/t/isochrones-with-the-option-avoid-polygone-are-larger-than-without/6669>\
**Category:** isochrones\
**Created:** [November 14, 2024, 11:51pm UTC](https://ask.openrouteservice.org/t/isochrones-with-the-option-avoid-polygone-are-larger-than-without/6669 "2024-11-14T23:51:34Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![JonasW](https://ask.openrouteservice.org/letter_avatar_proxy/v4/letter/j/8dc957/32.png) [@JonasW](https://ask.openrouteservice.org/u/JonasW)\
**Post date:** [November 14, 2024, 11:51pm UTC](https://ask.openrouteservice.org/t/isochrones-with-the-option-avoid-polygone-are-larger-than-without/6669/1 "2024-11-14T23:51:34Z")

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Hello,

I have a question how the ORS algorithm is working. I created isochrones from a point layer and in the second step I did it again with the same parameters but now with the option “avoid polygones”.

For most points it worked well, but some isochrones were larger (area and population) after the second run than after the first run.

From my point of view this cannot be.

Is there an answer for this problem? Or did I make a mistake?

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**Author:** ![andrzej](https://ask.openrouteservice.org/user_avatar/ask.openrouteservice.org/andrzej/32/10_2.png) [@andrzej](https://ask.openrouteservice.org/u/andrzej)\
**Post date:** [November 15, 2024, 6:58am UTC](https://ask.openrouteservice.org/t/isochrones-with-the-option-avoid-polygone-are-larger-than-without/6669/2 "2024-11-15T06:58:23Z")

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Hi,

thanks for reaching out. Could you maybe provide a concrete example illustrating the issue?

Cheers,  
Andrzej

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**Author:** ![JonasW](https://ask.openrouteservice.org/letter_avatar_proxy/v4/letter/j/8dc957/32.png) [@JonasW](https://ask.openrouteservice.org/u/JonasW)\
**Post date:** [November 15, 2024, 9:41am UTC](https://ask.openrouteservice.org/t/isochrones-with-the-option-avoid-polygone-are-larger-than-without/6669/3 "2024-11-15T09:41:39Z")

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Hello,  
here are some pictures of the issue.  
And here is also a link to the dataset of two points and the avoid polygones.

> **[Example\_AvoidPolygones](https://heibox.uni-heidelberg.de/d/d81e4412abe84848ac7a/)**
>
> Share link for Example\_AvoidPolygones.

 ![Avoid Polygones](https://ask.openrouteservice.org/uploads/default/original/2X/4/4eed6c8ae8561a0b7202ac350c5434255ff354a6.png)  
 ![With Avoid Polygones](https://ask.openrouteservice.org/uploads/default/original/2X/c/cf75e8aa92a76c11d6b3521dc52fef2d235016b2.png)  
 ![Without Avoid Polygones](https://ask.openrouteservice.org/uploads/default/original/2X/3/3d3abfb3353c0bdc0e813793a61907c7283d65f0.png)

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**Author:** ![andrzej](https://ask.openrouteservice.org/user_avatar/ask.openrouteservice.org/andrzej/32/10_2.png) [@andrzej](https://ask.openrouteservice.org/u/andrzej)\
**Post date:** [November 15, 2024, 2:17pm UTC](https://ask.openrouteservice.org/t/isochrones-with-the-option-avoid-polygone-are-larger-than-without/6669/4 "2024-11-15T14:17:54Z")

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Thanks a lot! Would you mind providing the parameters of the isochrones you are trying to compute as well, such as profile, range, etc? Cheers!

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**Author:** ![JonasW](https://ask.openrouteservice.org/letter_avatar_proxy/v4/letter/j/8dc957/32.png) [@JonasW](https://ask.openrouteservice.org/u/JonasW)\
**Post date:** [November 15, 2024, 3:08pm UTC](https://ask.openrouteservice.org/t/isochrones-with-the-option-avoid-polygone-are-larger-than-without/6669/5 "2024-11-15T15:08:01Z")

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Parameters:  
Travel mode: driving-car  
Dimension: time  
Range: 30  
Location Type: destination

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<div class="post-metadata">

**Author:** ![JonasW](https://ask.openrouteservice.org/letter_avatar_proxy/v4/letter/j/8dc957/32.png) [@JonasW](https://ask.openrouteservice.org/u/JonasW)\
**Post date:** [November 21, 2024, 10:23am UTC](https://ask.openrouteservice.org/t/isochrones-with-the-option-avoid-polygone-are-larger-than-without/6669/6 "2024-11-21T10:23:49Z")

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Do you have a solution for this problem now?  
Thanks a lot.

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**Author:** ![andrzej](https://ask.openrouteservice.org/user_avatar/ask.openrouteservice.org/andrzej/32/10_2.png) [@andrzej](https://ask.openrouteservice.org/u/andrzej)\
**Post date:** [November 22, 2024, 10:10am UTC](https://ask.openrouteservice.org/t/isochrones-with-the-option-avoid-polygone-are-larger-than-without/6669/8 "2024-11-22T10:10:12Z")

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Hi @JonasW,

thanks for your patience. I was able to reproduce the described behavior, very puzzling indeed! Unfortunately, I neither have an explanation nor a solution currently. The exact cause needs to be investigated. I’ll keep you posted.

Cheers,  
Andrzej

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**Author:** ![JonasW](https://ask.openrouteservice.org/letter_avatar_proxy/v4/letter/j/8dc957/32.png) [@JonasW](https://ask.openrouteservice.org/u/JonasW)\
**Post date:** [November 22, 2024, 10:27am UTC](https://ask.openrouteservice.org/t/isochrones-with-the-option-avoid-polygone-are-larger-than-without/6669/9 "2024-11-22T10:27:55Z")

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All right.  
Thank you for your answer.