I have a grid with cells of 0.5*0.5 decimal degrees. I am aware of the problem that the cells change in size and would like to take care of it. Exporting my data with "Export Feature Attribute to ASCII" results in the above mentioned warning.
Therefore, I followed the advice and used the "project" tool. I put in the dataset, selected the same coordinate system as before (GCS_WGS_1984), clicked on "preserve shape" and defined the maximum offset as 1 kilometer. However, I still receive the same warning as before.
What do I have to do to receive an accurate result?
GCS_WGS_1984 is a geographic coordinate system whose units are in decimal degrees. You need to select a projected coordinate system appropriate for your area and areal coverage. Something like a UTM or the dismal Web Mercator
Still, the results confuse me even more: I have to analyse the entire world, not just one section, so I chose the WGS_1984_Web_Mercator_Auxiliary_Sphere. When I click on a cell close to the equator it shows the proper area of about 3,000,000,000 (55km times 55km), but when I go far to the North the stated area increases about threefold...
But it should be the other way around, should it not? The grids become smaller in the North, so it should give me a smaller area.
if you want an equal area, then you need an equal area projection. If you are working with featureclasses, then you can calculate area using Add Geometry Attributes I am not sure that clicking around is what you need, perhaps a featureclass with the information calculated properly, then use the information within the tables.
I totally agree that clicking around is not optimal. Unfortunately this is what I usually have to do, given that my formal ArcGIS education consists of a one-week course (which I took three years ago).
"Add Geometry Attributes" seems to have worked wonders! I selected "Geodesic area" and specified length "kilometers" and area unit "square kilometers". Now it gives me an area that seems to be very much in line with expectations.
