topic Re: Calculating area of polygons in Data Management Questions https://community.esri.com/t5/data-management-questions/calculating-area-of-polygons/m-p/236314#M13404 <HTML><HEAD></HEAD><BODY><P>To find out what is what. I would suggest that you calculate area fields using your national grid projection, then another field using a web Mercator projection and finally one which is in GCS WGS84 aka, decimal degrees.</P><P>One of those three columns showing the area calculations should match what is being shown in AGOL.&nbsp; It is undoubtedly a projection issue that is giving rise to the variations.</P></BODY></HTML> Fri, 13 Apr 2018 16:20:30 GMT DanPatterson_Retired 2018-04-13T16:20:30Z Calculating area of polygons https://community.esri.com/t5/data-management-questions/calculating-area-of-polygons/m-p/236313#M13403 <HTML><HEAD></HEAD><BODY><P>I appreciate this topic has been covered before, but having reviewed various questions and tried to follow various suggestions I am still having problems.</P><P></P><P>I create content in ArcGIS Pro using British National Grid as the coordinate system and then create a hosted feature layer from it for others to use/add to in AGOL.&nbsp;</P><P></P><P>Area_Shape field is automatically generated, but as others have commented it doesn't match any of the area measurements when I measure the area of the polygon with the measure tool.&nbsp;</P><P></P><P>Can anyone give me step by step instructions for the best (least technical) way for me to get accurate area measurements in AGOL?</P><P></P></BODY></HTML> Fri, 13 Apr 2018 15:29:34 GMT https://community.esri.com/t5/data-management-questions/calculating-area-of-polygons/m-p/236313#M13403 SophieHorsley 2018-04-13T15:29:34Z Re: Calculating area of polygons https://community.esri.com/t5/data-management-questions/calculating-area-of-polygons/m-p/236314#M13404 <HTML><HEAD></HEAD><BODY><P>To find out what is what. I would suggest that you calculate area fields using your national grid projection, then another field using a web Mercator projection and finally one which is in GCS WGS84 aka, decimal degrees.</P><P>One of those three columns showing the area calculations should match what is being shown in AGOL.&nbsp; It is undoubtedly a projection issue that is giving rise to the variations.</P></BODY></HTML> Fri, 13 Apr 2018 16:20:30 GMT https://community.esri.com/t5/data-management-questions/calculating-area-of-polygons/m-p/236314#M13404 DanPatterson_Retired 2018-04-13T16:20:30Z Re: Calculating area of polygons https://community.esri.com/t5/data-management-questions/calculating-area-of-polygons/m-p/236315#M13405 <HTML><HEAD></HEAD><BODY><P>From a number of other threads, Web Mercator shouldn't be used for distance or area calculations.&nbsp; It is an inherent limitation of the projection</P></BODY></HTML> Mon, 30 Apr 2018 00:28:50 GMT https://community.esri.com/t5/data-management-questions/calculating-area-of-polygons/m-p/236315#M13405 DanPatterson_Retired 2018-04-30T00:28:50Z