topic Re: attribute length and shape lenght are not the same in Transportation Questions

attribute length and shape lenght are not the same

MatthiasWüthrich — Mon, 26 Mar 2018 17:09:24 GMT

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.

Re: attribute length and shape lenght are not the same

DanPatterson_Retired — Mon, 26 Mar 2018 17:23:07 GMT

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

Re: attribute length and shape lenght are not the same

MatthiasWüthrich — Mon, 26 Mar 2018 17:35:10 GMT

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

Re: attribute length and shape lenght are not the same

DanPatterson_Retired — Mon, 26 Mar 2018 17:39:30 GMT

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

Re: attribute length and shape lenght are not the same

MatthiasWüthrich — Mon, 26 Mar 2018 17:52:58 GMT

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.

Re: attribute length and shape lenght are not the same

DanPatterson_Retired — Mon, 26 Mar 2018 18:59:58 GMT

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 )?

Re: attribute length and shape lenght are not the same

AbdullahAnter — Mon, 26 Mar 2018 19:47:38 GMT

Where is the location of measure? (the country )

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

Re: attribute length and shape lenght are not the same

MatthiasWüthrich — Mon, 26 Mar 2018 20:27:06 GMT

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.

Re: attribute length and shape lenght are not the same

DanPatterson_Retired — Mon, 26 Mar 2018 20:43:07 GMT

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' .

Re: attribute length and shape lenght are not the same

AbdullahAnter — Mon, 26 Mar 2018 21:21:56 GMT

Using wrong projection in Switzerland cause a massive error .

If the shape_length is the standard field with feature class in geo-database, that always is correct one as long as you using the correct projection.

in your case you should use projection provide a correct distance such as (WGS_1984_UTM_Zone_32N / Bern_1898_Bern_LV03C)

Re: attribute length and shape lenght are not the same

JaySandhu — Mon, 26 Mar 2018 21:40:35 GMT

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

Re: attribute length and shape lenght are not the same

JaySandhu — Mon, 26 Mar 2018 21:43:14 GMT

Read the following for more info on distance errors with web mercator:

https://blogs.esri.com/esri/arcgis/2010/03/05/measuring-distances-and-areas-when-your-map-uses-the-mercator-projection/

Update:

The above link is not available as the Esri blog site has changed. See the link that Dan Patterson has posted for the technical support article.

Re: attribute length and shape lenght are not the same

MatthiasWüthrich — Tue, 27 Mar 2018 18:55:14 GMT

Problem was web mercator. Transformed it and now everything is fine. Thanks alot.

Re: attribute length and shape lenght are not the same

DanPatterson_Retired — Sat, 28 Apr 2018 16:02:02 GMT

Jay... the link goes to the general page...

perhaps this can substitute until you can locate it ... Why are my map, distance and area measurements wrong when using WGS 1984 Web Mercator?

Re: attribute length and shape lenght are not the same

DanPatterson_Retired — Sat, 28 Apr 2018 16:02:49 GMT

Why are my map, distance and area measurements wrong when using WGS 1984 Web Mercator?

Re: attribute length and shape lenght are not the same

AdrianWelsh — Sat, 28 Apr 2018 16:13:25 GMT

This is a good article! (too bad that all online maps have to use this projection).

Re: attribute length and shape lenght are not the same

SanneMikkelsen — Fri, 31 Jul 2020 07:47:28 GMT

I have the same problem in ArcGIS online. The layer is created in online, and the distances differ x2. I thought that it would be the same projection, when my user uses AGOL for it all. How do i transform it in AGOL?