what to input for ???in_value_raster??? in zonal statistics as table

[ElaineKuo]

System ArcGIS 9.3

I have some polygon shape files of bird distributions.
Each file has two groups of distribution types: summer and winter.
For each distribution type,
I want calculate the average monthly temperature respectively.

Some seniors have advised to use zonal statistics as table,
since I have feature datasets.
However, one of the input fields of zonal statistics as table confused me.
It was ???in_value_raster???.
I do not know which raster file to be input,
because I only have feature datasets at hand.

According to ArcGIS Desktop help,
two possible solutions are ???feature to raster??? or ???polygon to raster.???
However, I found their output cell sizes were different.
The one of ???feature to raster??? was 16762,
and the other ???polygon to raster??? was 17000.
(The original feature datasets has grid cell size around 100 km in Behrmann projection.)

Please kindly help with the following questions and thank you in advance.

Questions:
1. Please kindly advise if it is possible to input feature datasets or the alternative in the field ???in_value_raster??? without converting shapefile into raster data sets in advance. (in order to want to save space storing raster datasets)

2.  Please kindly advise why the output cell sizes could be different using ???feature to raster??? or ???polygon to raster.??? Which output cell size is more close to the original cell size? Why?

3.  How to make the output cell size of raster dataset the same as the original   shapefile?

[EricRice]

Elaine,

The in_value_raster parameter would be the temperature rasters that you are trying to get the average monthly temperature of per polygon.  This would require you to have 12 temperature rasters; one for each month.  Each time you execute the tool it would return the average (mean) temperature per "Input feature zone data".

Regards,
Eric

[ElaineKuo]

Thank you for the response.
Now another question conjured up.

Please kindly advise why the output cell sizes could be different using �??feature to raster�?� or �??polygon to raster.�?�
Which output cell size is more close to the original cell size? Why?
Shall I pay attention to anything on cell size when converting polygon to raster?

[EricRice · Accepted solution]

It's not required of you to convert the polygons to raster in advance, although it will make the zonal tool faster since it won't have to do it.  When you let the software convert the polygon zones to raster, it will convert it using the same cell size as the input value raster.  If the zones (this whole part is in the doc) are relatively small (especially when smaller than a single pixel in the value raster) we do suggest you determine a more appropriate cell size to use, so as to not lose a zone in the conversion process.

So, if your temperature raster is very coarse resolution relative to the size of a single zone, you should convert the zone data to raster at a cell size finer than the temperature raster. The cell size needs to be determined by you.  That is, you need to determine a small enough cell size to represent the polygon while in raster form.  Technically, once you determine the appropriate cell size to represent the features, you don't have to convert the polygons into rasters at that resolution (unless you want the tool to run faster). You can just use this resolution as the cell size in the Raster Analysis Settings of the Environment Settings.

Please review Zonal Statistics As Table for many more details.

Eric