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I am a newbie with raster data. Maybe this is a trivial question. Can a single pixel of a raster hold more than one value?

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This sounds like three valid Questions which I would recommend splitting. –  PolyGeo May 19 '13 at 6:38
    
@PolyGeo Actually these question come in my mind all together. So, I thought somehow they are related. So I asked those all together. And now after your I think they can be different questions. But should I split it now?? –  Emi May 19 '13 at 6:44
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I always find "one question, one answer" easier to read and a cut/paste should make the split straightforward to do. –  PolyGeo May 19 '13 at 6:58
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3 Answers

up vote 6 down vote accepted

A pixel can only hold one value, but if the resultant grid is an integer grid, then an attribute table will be created. If the grid is a floating point grid, then no table is created. See comments in your related questions.

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You can encode multiple values in raster data using bit flags. This is how MODIS data stores quality and cloud masks. Bitwise operators can be used to extract these values.

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I may be wrong here but it is as simple as that- 8-bit integer raster hold 2^8 information space (value space). We can use this space in variety ways ie. finding some fancy coding system/flags/pattern stuff (some time ago I saw Whubers methods for encrypting information in vector geomtries!), but we will not be able to put in a cell anything else outside 0-255 range (I guess that is for unsigned integer). So, the answer depends on, what do you actually mean by value. You can have 3-band raster which would hold 3 values for the same pixel at raster level, but at band level (which is exacly 2D array-raster) you have again one space described by your raster data type.

Attribute tables are not directly connected to certain pixel (not like .shp). They collect info about classes and pixel count in class in the raster. Do not refer to any particular cell.

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