# Interpolation from isolines vs Thiessen (Voronoi) polygons interpolation

I'm currently studying GIS and have come across a question in an assignment that I just can't answer. I've been googling my brains out for the last few hours and got nowhere... here goes...

Identify two (2) similarities and two (2) differences between (i) interpolation from isolines and (ii) Thiessen (Voronoi) polygons interpolation. Explain your answer.

Any ideas or know somewhere to point me where I might find the info?

• Welcome to GIS SE! As a new user be sure to take the Tour. While we do not have a policy against homework questions, we do ask that you provide evidence for having undertaken research prior to asking here. In this case I would have thought the absolute minimum would be references to definitions for "interpolation from isolines" and "Thiessen (Voronoi) polygons interpolation" and your first thoughts on what might be some similarities and differences between them.
– PolyGeo
Commented Aug 21, 2015 at 5:53
• +1 for clearly identifying that this is homework. It seems as though you're not after an answer but rather a hint to go looking for an answer which is totally the right thing to do... unfortunately I can't help comparing the two methods; perhaps think of synonyms for these methods (like IDW) - it's all a bit theoretical for me. These sorts of things usually come back to what was said in class or what is in your texts so that would be the first place to look. Commented Aug 21, 2015 at 5:54
• I know exactly what you mean by Thiessen, but would you expand on the isoline interpolation? How exactly would you interpolate from the isoline values? Commented Aug 21, 2015 at 15:53
• @PolyGeo Thank you all for your comments. Sorry, I didn't realise I had to provide evidence of prior research... I have read and reread the study book that was provided with the course which isn't giving me any clues regarding similarities, google wasn't much help either. (I have managed to come up with a few differences from definitions in the study book)
– Jen
Commented Aug 25, 2015 at 5:41
• @Michael Miles-Stimson Thank you for suggesting the synonyms method, the study book with the course doesn't mention any synonyms.
– Jen
Commented Aug 25, 2015 at 5:41

I happen to be studying the same subject. The two are both different examples of interpolation. Let me clarify what the terms refer to in this context.

### Interpolation from isolines:

Using isolines (such as contours) to produce a DEM. The Topo to Raster in the Spatial Analyst extension to ArcGIS is an example (http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=Using%20the%20Topo%20to%20Raster%20tool).

### Thiessen (Voronoi) polygons interpolation:

Using point data to create Thiessen proximal polygons. The Create Thiessen Polygons (Analysis) tool in ArcGIS is an example (http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?id=1274&pid=1272&topicname=Create_Thiessen_Polygons_(Analysis)).

Finding similarities is much harder than finding differences! The two links provided might be a good place to start...

• Thank you for your comment and supplied links, I will check them out. :) Yes, I have managed to find a few differences but I am struggling with the similarities as you mentioned. Being an external student I am have some troubles understanding the more complex analysis techniques and the fact that this assignment is more about application of techniques and isn't fully explained in the study book itself is frustrating. I will keep at it though.
– Jen
Commented Aug 25, 2015 at 5:30