topic Re: Different area calculated between shapefiles and geodatabase in Data Management Questions

Different area calculated between shapefiles and geodatabase

lawrencegalakong — Mon, 11 Mar 2013 07:49:33 GMT

Hi. Our company recently purchased the ArcGIS Server. We migrated all of our GIS data from the native Shapefiles format to GeoDatabase. the problem, we get 2 different areas - hectares calculated in shapefiles are different than those calculated in the GeoDB. Does anybody have this problem? is this normal? because we have to explain the difference to our management.

Thanks.

Re: Different area calculated between shapefiles and geodatabase

DanPatterson_Retired — Mon, 11 Mar 2013 08:00:09 GMT

Are the differences huge? or could they be the result of precision differences? Some example values would help

Re: Different area calculated between shapefiles and geodatabase

LeoDonahue — Mon, 11 Mar 2013 14:45:23 GMT

I posted something similar to this a long time ago. http://forums.arcgis.com/threads/17049-Buffer-getArea%28%29

I noticed that depending on how the data is stored and how you are calculating the area, you get different results. For us, the area was different using FGDB vs SDE and ArcMap vs ArcObjects.

I think a few years ago ESRI admitted online somewhere that Shapefile storage was not as good as FGDB during the marketing for the new file formats. I wouldn't use Shapefiles anymore for anything relating to calculating area.

Re: Different area calculated between shapefiles and geodatabase

lawrencegalakong — Wed, 20 Mar 2013 04:49:44 GMT

Are the differences huge? or could they be the result of precision differences? Some example values would help

hi. the area difference is shown below. hectares are stored in a field with Double (10,2) format.

Hectares in GeoDb = 48,597.64
Hectares in Shape = 48,615.66
Difference = 18.02

Re: Different area calculated between shapefiles and geodatabase

DanPatterson_Retired — Wed, 20 Mar 2013 05:53:10 GMT

create a feature of known dimensions (ie a rotated rectangle) and save it in the various formats you work with and calculate the coordinates, perimeter and area of said feature. i have never found shapefiles to yield erroneous dimensions in either location, perimeter or area

Re: Different area calculated between shapefiles and geodatabase

lawrencegalakong — Thu, 21 Mar 2013 08:07:02 GMT

hi dan. i think i know what the problem is. we're taking area (hectares) only to 2 decimal points, and when ArcGIS calculates the area, it takes the value to 2 decimal points without considering the value of the third decimal point; 2.1588 should be 2.16, but it returns 2.15. Please see the image below: -

[ATTACH=CONFIG]22823[/ATTACH]

"HECTARES" -> stores the area calculated in shape format using the Calculate Geometry function
"HA2" -> stores the area calculated in geodb format using the Calculate Geometry function
"HA3" -> stores the area calculated by dividing "SHAPE.STArea()" with 10000

is there any workaround for this? thanks.

Re: Different area calculated between shapefiles and geodatabase

LouiseDuffy2 — Wed, 24 Apr 2013 21:33:08 GMT

Just wondering if you have gotten an answer to this.