Take the 2-minute tour ×
Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. It's 100% free, no registration required.

Specifically, I have a rainfall map (Isohyets) measured in mm (precipitation)... I wanted to know a particular value (precipitation) at any point between these lines...

How can I do this? Do I have to convert/interpolate these polylines so I could have a Rainfall raster instead? So that I would know the precipitation in any point based on cell values of the Rainfall raster? If so, how do I make a raster map out of my rainfall contours/isohyets? By the way, I have a DEM of 20-m resolution.

Will this be of any help in converting/interpolating my rainfall map?

share|improve this question
1  
Yes, you'll need to interpolate to get a precipitation estimate at arbitrary points. Note that isohyets themselves are already either an interpolation of the original point measurements (from gauges) or a subset of distributed measurements (from remote sensing), so ideally you would go from that data directly instead of using the intermediate step of the isohyets. Do you know how the isohyets were generated? –  Jake Feb 5 '13 at 9:52
    
Hi Jake! Thank you so much for helping me out,... Yes, the isohyets must have come from gauging points..But unfortunately, I only have the isohyets. I don't have the original point measurements...Does this mean a "dead-end" for me? :( How about converting from feature to raster through "mapping density" out of my polylines (isohyets)? Is this valid analysis? I'm not sure,.. Hope to hear from you soon,..Thanks again.Be safe. –  Joanne Feb 6 '13 at 4:18
    
What you want to do is very doable in ArcGIS. If you have access to 3D Analyst you can convert it to TIN or raster (with Spatial Analyst I think it is only possible to make raster). If chosen interpolation (to raster) technique does not support your polylines, you can always extract points from polylines. I your case I would use TIN or TOPO to Raster or spline interpolation, but there maybe some other fancy interpolation algorithm more suitable for isohyets precipitation data. –  Tomek Feb 6 '13 at 6:55
    
@Joanne: Yes, you can definitely interpolate between contour lines, it just takes a bit of consideration because the data is so unevenly distributed. GRASS (an open source GIS) has a couple of interpolation algorithms which are compared regarding their suitability for interpolating between contour lines at grasswiki.osgeo.org/wiki/Contour_lines_to_DEM. Generally, r.surf.contour tends to work quite well. –  Jake Feb 6 '13 at 8:39
    
This Question has been out for over a year but despite some suggestions, no Answer has been offered. In any event the Question includes 5 question marks so the precise question being asked is hard to discern. –  PolyGeo Apr 12 at 4:59
add comment

closed as too broad by PolyGeo, Simbamangu, Devdatta Tengshe, BradHards, Fezter Apr 12 at 10:40

There are either too many possible answers, or good answers would be too long for this format. Please add details to narrow the answer set or to isolate an issue that can be answered in a few paragraphs.If this question can be reworded to fit the rules in the help center, please edit the question.