Calculating averages using point data: Desperate for assistance!!!!

[TravMoore]

Hi,

I currently have a global map shapefile, superimposed by 8192 data points that show temperature changes (per degree Celsius of global warming) and degrees of latitude/longitude at those locations on the globe. So, for instance, an individual data point would say (when using the "Identify" function) at 180 West, 45 degrees North, the temperature change per degree Celsius global warming is 0.8 Celsius. Each of the 8192 points contain this sort of data.

What I am attempting to do is simply calculate various averages for different regions by somehow combining the necessary points over those regions. For example, if I would like to calculate the average temperature change in the United States, how could I do this using the point data that covers the United States?

Any assistance would be greatly appreciated!

Patiently awaiting your response(s),

~Trav.~

[TravMoore]

Hi Caleb/Srirama,

Okay, I've done as was instructed with respect to "Spatial Join" and successfully acquired a new attribute table. I've tried joining the temperature point data (Target Feature) and "country name" or "Continent" (so, two attempts), based on the world map that I have (see attached file above) - however, under "Continent", for example, I noticed that for many rows, they say "<Null>". Some rows actually show the actual continents, but most are nulls. Is there a reason for that?

Now, if I want to simply acquire the annual temperature means for, say, Antarctica, how may I do this using the attribute table? I understand that you had mentioned right-clicking on the "Continent" column, for example, and then select "Summarize" in the drop down menu. However, how may I only select the Antarctica rows, and then acquire an average based on those selected rows?

Thanks again, and I apologize for the questions!

~Trav.~

Edit: Bill, thank you for your input. Would it be possible to show me a detailed procedure in doing this in ArcGIS? If so, I would greatly appreciate it!

[Anonymous User]

Those null values are most likely coming from the points that are not overlapping with the continents (aka the points over the oceans).  Since the continents do not intersect the points over the oceans, there is no continent value for those rows (thus giving you null values).  You can still summarize the table by the continents field though to find your averages.

Also, Bill made a great point and weighted averages would probably be a good idea.

[TravMoore]

Hi Caleb/Bill,

I believe that you may be correct about the nulls representing mostly oceans, or bodies of water. However, I noticed that there aren't a great deal of rows covering the continents (for example, the number of rows covering South America is less than the actual number of points covering that continent). Antarctica, though, has a comparatively large amount of rows. Could there be a reason as to why?

Now, if I wanted to select only the Antarctica rows in the resultant table (from the spatial join), for instance, how may I do this to calculate the annual average for Antarctica?

As for Bill's suggestion, this had also been stated to me previously, as well. However, I have absolutely no idea where to begin in calculating weighted averages. I took a look at the link that Bill provided, but I quickly became lost, unfortunately. Is there a way to obtain detailed step-by-step in order to compute weighted averages? I am really interested in going through with this!

Many thanks,

~Trav.~