attribute length and shape lenght are not the same

[MatthiasWüthrich]

Hello

I have an attribute table which contains shape_length and attribute_length. The table was created by the Copy traversed source features tool. Attribute length is correct, but shape length is about 1.5 times bigger for the same attribute. If I measure any distance on the map, and compare it to measurements I did on Google maps, the distance is also 1.5 times as big as on Google maps. I guess that this will be a spatial reference issue. I transformed all my data into wgs_1984_web_mercator_auxiliary_sphere. I know that wgs84 isn`t very accurate, but a factor of 1.5 seems to be much more than simply inaccurate.

Any suggestions? Thank you.

[DanPatterson_Retired]

not a feet versus meters thing then? But what are your actual units anyway?

[MatthiasWüthrich]

I`m using meters. I set the units to meters, so this should not be the problem.

[DanPatterson_Retired]

When you say 'set' .... you set the display? you projected your data?  A factor of 1.5 doesn't ring a bell, so you native units in the file could be different (ie decimal degrees) or something else

[MatthiasWüthrich]

Yes, I projected my data. When I check my dataframe properties, it shows me that all layers are all in the same coordinate system (wgs84). The units I set also in dataframe properties and in networkanalyst settings, both meters. When I use the small ruler icon to measure something, it tells me also that unit is meters. The source files are all in meters. Thanks for your help.

[DanPatterson_Retired]

WGS84 is a datum, not a coordinate system. 

Are the data a GCS WGS84 (aka decimal degrees) or some projected coordinate system with a WGS84 datum (like the web thing )?

[AbdullahAnter]

Where is the location of measure? (the country )

How do you get the attribute length and How you know that is the correct one?

[MatthiasWüthrich]

projected coordinate system is wgs1984 webmercator auxiliary sphere, geographic coordinate system gcs wgs84.

Country is Switzerland. I compared measures I made on arcgis with ones i made on google maps. I know think that wgs1984 is simply not made to measure something.

[DanPatterson_Retired]

geographic coordinate systems will return measures in degrees or fractions of a degree in arcmap, unless the dataframe (or map in PRO) is set to return measures in your desired coordinate system.  Dataframes in arcmap, take on the coordinate system of the first layer added to it, which is why you need to explicitly set a coordinate system (or projection) if you intend to rely on 'projection-on-the-fly' .

[JaySandhu]

It is to be expected. See the screen shot I am attaching. The red lines are projected to web mercator and the blue lines are in Lambert conformal conic. For the selected edge, the web mercator distance is 115.7 meters and the lambert conformal is 77.7 meters. The difference is about 1.5 times more in web mercator.

Jay Sandhu