Has anyone had issues before with calculating areas in ArcGIS Online / FieldMaps? I have a polygon layer with these details:
Is there a way I can get the layers on ArcGIS Online to auto-populate with the correct 10,854.62 value for the Web Mercator layers? The field workers would like to see the area while they're capturing polygons on site in real time. We have 1000s of layers in Web Mercator so would prefer not to have to reproject them all to ITM. It is also confusing when the Shape__Area field is giving an incorrect value on the ITM layers.
Nicola,
I too have had issues with measurements in AGOL versus anything else and my rule of thumb is to NEVER use AGOL to properly and accurately measure anything. I work with surveyors where accuracy and precision are very important. We have found that the best way to represent anything regarding measurements is to have a 'static' field in the feature that gives the correct measurements that the user needs to see.
Thanks,Adrian
Me too. Don't trust any measurements from the measurement widget or the draw widget (even if using tool tip contraints, still won't be accurate). I have put dozens of reqeuests to re develop the measurement widget and it never seems to be implemented. There was a brief time where Esri acted like the Draw widget would take care of my measuring concerns, then I documented that didn't work either and never heard much back.
The measurement widget gives the correct answer for us, it matches what's calculated in ArcPro, but the Shape__Area gives a wildly incorrect answer no matter what projection system is used...
Thanks Adrian. By 'static' do you mean it's calculated separately outside of AGOL and then put onto AGOL? Our issue is we have surveyors on site creating polygons and they want to see the area on the go, but the Shape__Area attribute is wrong no matter what projection system is used, and the Arcade expressions are also wrong when using Web Mercator (though ArcPro has no issue calculating the correct area when a layer is in Web Mercator) and it would be a bit of a hassle to reproject 100s of active layers to ITM, reupload, and add new fields with Arcade expressions to all of them (while also making sure surveyors don't get confused with the Shape__Area field)
Yes, static meaning to calculate them outside of AGOL. I would never have surveyors create polygons in an app or in the field, and expect them to be accurately measured. The surveyors I know would lose their mind of over this, haha! Many surveyors do not see GIS as an 'accurate' measuring tool so they know that when calculating areas in GIS that they will not get the desired results. Typically, all AGOL maps are in WGS84 Web Mercator, which is the main source of the issue, that I have found. You would need another mapping application to give you more accurate, in-field measurements. Perhaps a Portal system could be in your native projection but I'd still be cautious of its measurements.
Don't show surveyors the shape_area field. Hide that one. It only causes problems.
The measurement is accurate using the Arcade expression AreaGeodetic($feature, 'square-meters') in a field when the when the layer is in ITM, it doesn't matter what map it's on as a layer could be on multiple maps, so it wouldn't really be as much of an issue if all of our layers were in ITM. Unfortunately most of the layers are in web mercator which is where the main issue is. Not sure why it's an issue when ArcGIS Pro can calculate accurate areas with web mercator, surely they should be using the same system across platforms for calculating geometries!
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