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2

Here's how you can get Shape.area to display acres if it's in another unit. In ArcMap, go to the layer properties and the Fields tab. Under "Appearance", click "Number Format". Click the little button with the ellipses that is now displayed. Or right-click a field name in the table view, go to Properties, and click the little ellipses button next to ...


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The simple answer might be that changes to your polygon layer will not be confirmed until you save our edits. Make sure you save your edits between creating your ring and doing your area calculation. I believe it is possible to create automatically updating area fields in QGIS 2.4, but I haven't been able to do it myself as it requires a bit of Python. ...


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I would do this in two steps. Firstly add a new field to contain the area of your polygons (see below) give it a basic name such as Area and make the type double (see this for more details). You can then calculate the geometry of your polygons in your new field by right clicking the field heading and selecting Calculate Geometry. Which will bring up the ...


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This sounds like something I would investigate using the Data Comparison toolset to assist with: The Data Comparison toolset contains tools to compare one dataset with another dataset to report similarities and differences. You can use these tools to identify changes made to a dataset. In particular the Detect Feature Changes tool which: Finds ...


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Assuming ArcGIS, here is an example Python Addin that calculates areas: class CalculateArea(object): """Implementation for Test_addin.calculateArea (Button)""" def __init__(self): self.enabled = True self.checked = False def onClick(self): # Set mxd to current and data frame to active mxd = ...


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By design Shapely is unaware of coordinate reference systems or units. To use it to solve real world problems, you must learn to transform longitude and latitude to an approximately planar local reference system (like a US State Plane) and you must keep track of your own units. I use pyproj to do this, but you can use whatever you want. Once you've ...


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You may use: pythonaddins.MessageBox() See links below for examples: Getting results from your Python Add-in buttons The pythonaddins module


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Here is the result I derived for the rhumb line area. This is the more interesting result. The great ellipse formula is more complex and is very similar to that for geodesics. Consider a rhumb line from (φ1,λ1) to (φ2,λ2). Determine the area of the ellipsoidal quadrilateral whose sides are this rhumb line segment, two meridional ...


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This python package (written by me!) allows you to compute the area of a polygon on an ellipsoid. So just compute a set of latitude/longitude points around your ellipse and pass these to the area routine. There's no need to project the points. Brief documentation is available here. An online area calculator is available at this link.


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The quickest way that I am aware of, is to use the Shapely library (requires the GEOS Engine, you can find a one-click installer for shapely here if you're on windows) The manual provides a dead-on example of what your question: >>> from shapely.geometry import Point >>> a = Point(1, 1).buffer(1.5) >>> b = Point(2, ...



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