topic Re: How do I sum the areas of polygons in multiple shapefiles? in New to GIS Questions

How do I sum the areas of polygons in multiple shapefiles?

StephenWheeler — Wed, 18 Feb 2015 01:55:52 GMT

Hi All -- I have multiple geodatabases each with many shapefiles containing multiple polygons. I want to quickly and easily get the total area of polygons in each shapefile. I can't believe that ArcGIS is so cumbersome as to require me to add an Area field to each shapefile, calculate geometry, and then run statistics. Isn't there some simpler way to find out total area for each shape file?

Thanks so much for anyone's help! -- Steve Wheeler, U.C. Davis

Re: How do I sum the areas of polygons in multiple shapefiles?

DarrenWiens2 — Wed, 18 Feb 2015 03:09:51 GMT

You can certainly automate the process with python (if that's how you want to go, please indicate).

However, if your data truly are in geodatabases (there is some confusion whether you're talking about geodatabases or folders of shapefiles), each feature class will already have the auto-populated field SHAPE_AREA. Then, right-click the field and Summarize to get the total, or batch process Summary Statistics on all feature classes to semi-automate the totals.

Re: How do I sum the areas of polygons in multiple shapefiles?

DanPatterson_Retired — Wed, 18 Feb 2015 03:34:33 GMT

Not to mention the fact that some of the files will be using data in longitude and latitude. This will require you to project the data, which in turn can yield slightly different values for the same area, particularly if the datums are different. And we can't not mention that these calculations are all being done using some perhaps erroneous representation of true space...of course assuming everything was digitized and processed without error at the highest precision possible in the first place. So it is no wonder that people that study coordinate systems, projections and their implications to geometric representation of space have a hard time sleeping at night. And the poor surveys that have to collect these data with a high degree of accuracy only to have some cartographer cut corners...literally and figuratively... to make a map look better.

So my hat is off to people in that field of spatial data collection, geodesy and mapping like Melita ... Melita Kennedy‌

Then you raise that dreaded word ... statistics ... with the problems of collecting and representing space... someone wants to derive statistics. It is bad enough that they will attempt to derive meaningful descriptive statistics ... nope...they don't stop there ... off they go trying to show spatial patterns or that things are different and ascribe a reason for it.

When will the madness end? Grab a bunch of files in digital form for the same area ( a county perhaps) determine their geometry...take their average...and say 'about this big' ... or 'we will need more money to fine-tune the estimate'. So if you are on the receiving end of a request like this ... good luck ... if you are on the requesting end ... consider the above.

In jest of course ... or maybe some of it .

Re: How do I sum the areas of polygons in multiple shapefiles?

DarrenWiens2 — Wed, 18 Feb 2015 04:57:47 GMT

^ but chances are it's not that bad

Re: How do I sum the areas of polygons in multiple shapefiles?

StephenWheeler — Wed, 18 Feb 2015 05:23:57 GMT

Hi Darren -- Thanks so much for your answer. Probably the data is just in folders of shapefiles (not sure the exact definition of geodatabase). There isn't any SHAPE_AREA field on them. I don't know Python and don't want to get involved with scripts unless absolutely necessary....was hoping that at this point in its evolution ArcGIS was user-friendly enough to have some function to calculate area, which seems like such a basic thing.....What do you recommend?

Many thanks -- Steve

Re: How do I sum the areas of polygons in multiple shapefiles?

DanPatterson_Retired — Wed, 18 Feb 2015 08:52:00 GMT

Oh they exist...ArcScripts 2.0 is coming soon...

Re: How do I sum the areas of polygons in multiple shapefiles?

StephenWheeler — Thu, 19 Feb 2015 06:16:44 GMT

Hi Dan — Thanks, but where do i find Batch Calc APL? I don’t see it anywhere.

Steve

Re: How do I sum the areas of polygons in multiple shapefiles?

JayantaPoddar — Thu, 19 Feb 2015 08:50:00 GMT

Hi Stephen,

In ArcCatalog, you could create a new File geodatabase (FGDB), and a feature dataset (Define an appropriate Projected coordinate system to it). You could then just import all the shapefiles to the feature dataset. This will take care of Creation of Shape_Area Field, and calculate geometry for all the feature classes.

Thanks,

Jay

Re: How do I sum the areas of polygons in multiple shapefiles?

StephenWheeler — Thu, 19 Feb 2015 16:42:33 GMT

Hi Jay — Thanks; that’s helpful. I’ll give it a try.

Steve

Re: How do I sum the areas of polygons in multiple shapefiles?

DarrenWiens2 — Thu, 19 Feb 2015 16:49:51 GMT

This wouldn't take too long to do per folder simply through the GUI and batch processing. One batch for Add Field (area), one batch for Calculate Field, and finally Summary Statistics to add up the areas. Of course, if you have many folders, you'd want to automate it with a model or script.

Re: How do I sum the areas of polygons in multiple shapefiles?

StephenWheeler — Thu, 19 Feb 2015 17:47:58 GMT

Hi Jay - I've now got the FGDB and have imported the shapefiles...do I run Summary Statistics? This gives me an invalid pointer error message.

Thanks, Steve

Sent from my iPhone

Re: How do I sum the areas of polygons in multiple shapefiles?

JayantaPoddar — Thu, 19 Feb 2015 18:11:43 GMT

Make sure to define statistics field and statistics type as sum in Summary Statistics.

Re: How do I sum the areas of polygons in multiple shapefiles?

XanderBakker — Sat, 11 Dec 2021 07:54:49 GMT

Although very late, but you could do something like this with some Python code:

import arcpy
import os
workspace = r"C:\Path\To\Your\Folder"

sum_areas = 0
cnt = 0
walk = arcpy.da.Walk(workspace, topdown=True, datatype="FeatureClass", type="Polygon")
for dirpath, dirnames, filenames in walk:
    for filename in filenames:
        cnt += 1
        shp = os.path.join(dirpath, filename)
        area = sum([r[0] for r in arcpy.da.SearchCursor(shp, ("SHAPE@AREA")) if not r[0] is None])
        sum_areas += area
        print "shp: {0} has area {1}".format(shp, area)

print "{0} polygon featureclasses found".format(cnt)
if cnt > 0:
    print "total area: {0}".format(sum_areas)
    print "mean area per featureclass: {0}".format(round(sum_areas / float(cnt),2))

Re: How do I sum the areas of polygons in multiple shapefiles?

StephenWheeler — Fri, 20 Feb 2015 05:39:36 GMT

Alas, this looks too complicated to use. There are quite a few steps for each file, and to find the answer I have to then open an output table, which I'm not sure how to do (opening it in catalog doesn't appear to give me the sum). I'm trying instead to open each attribute table in the new geodatabase and right-click on shape-area to get statistics. The main problem at the moment is getting the units right. I thought I had everything set to kilometres but the areas are coming out way too large.

I really appreciate your help.

Steve

Sent from my iPhone

Re: How do I sum the areas of polygons in multiple shapefiles?

DarrenWiens2 — Fri, 20 Feb 2015 06:08:52 GMT

Are your expected areas either 1,000,000 (meters) or 10,764,000 (feet) times too large, by chance?