How to create an average rainfall map that is continuous and not pixelated?

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04-14-2014 03:13 AM
NICOLENEWITTER
New Contributor
Hi,

I am having some trouble producing an average rainfall map for my country. Using a world shapefile, I have identified my country and clipped the corresponding annual precipitation (tiff. format) data however the clipped raster is very pixelated and is not suitable for displaying precipitation which is normally depicted as a continuous data on a map. I attempted to convert the pixelated raster to a continuous data by going to Properties > Display> Resample during display: Bilinear Interpolation but I ended up with the attached result.(see attachment for screen dump)

If you need me to provide any additional information to this problem please let me know. I would be grateful for any assistance.

Thank you.
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5 Replies
JimCousins
MVP Regular Contributor
The issue is that the global data is at too low a resolution (x, y pixel size). Either work with a different data set, or reprocess your data. Reprocessing will not improve data accuracy - this is limited by the source, but you can improve the visual display of the data.
Convert your data from raster to point, and then use Interpolation tools (ie: kriging or idw) to create a new raster, but set the cell size to a much smaller value. The interpolation will smooth the transition between the points. You can also set the display of the resulting raster to "bilinear interpolation" to smooth it further.
Best Regards,
Jim
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NICOLENEWITTER
New Contributor
Hi Jim,

Thanks for responding. I converted the clipped raster of my country to points and then use Kriging for the interoplation method to smooth the points however I am not sure how to use it to depict the annual precipitation of my country. I do not understand the meaning of the kriging values that I am getting as they have no correlation to the precipitation values and pattern for my country. I have attached what I have done so far.

Looking forward to your assistance. Thank you.
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JimCousins
MVP Regular Contributor
Try expanding your point dataset some, so you have data surrounding the border.
When you perform the interpolation, be certain that you set the correct value for "z-value".
Kriging will honor the input point values, so your data should accurately reflect the precipitation at these locations, and interpolate between them to fill gaps.
You could also set an analysis extent to prevent data from spilling way outside the realistic interpolation zone.
Regards,
Jim
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NICOLENEWITTER
New Contributor
Hi Jim,

My map looks much better. To expand my point dataset, I created 1000 random points, extract the values of these points using the clipped precipitation raster and then interpolate using Kriging.  I did some cleaning up of the map and the final map is attached.

I really appreciated your help. Thanks again!:)
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JimCousins
MVP Regular Contributor
Much better! Glad I could assist.
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