Scalebar value changes with map move

MichaelErlich · ‎09-01-2011

As you can see from the attached images, the scalebar shows 4 different values depending on where the map is dragged. The zoom level never changed and the map data was from a tile pack.

Anonymous User · ‎09-07-2011

Original User: mbranscomb

Hi,

Unfortunately I'm unable to reproduce this...

- Do you still see the issue with online services only?
- Are you able to provide some sample data and a sample app with which I can reproduce the issue? (if yes to the first question that would negate the need for sample data).

Cheers

Mike

Anonymous User · ‎09-07-2011

Original User: psiclopz

Hi Mike,

It's the same MergedWest tile pack that is on our FTP, and we're loading it locally. I see the same issue on my machine as well. It mainly seems to happen when zoomed in a couple levels and then moving from the western US and then panning towards Alaska. As you move from the Continental US to Alaska on the same zoom level the scale seems to change.

One of us could probably be able to put together a quick sample app if you still can't reproduce this with our data.

Thanks,

James

Anonymous User · ‎09-07-2011

Original User: kscholefield

Hi,

The ScaleBar Control has been deprecated so the recommendation is to use the ScaleLine control in the Toolkit. The ScaleLine control exhibits the same behaviour you were experiencing with the ScaleBar control because, by design the ScaleLine control takes the value at the centre of the map as the approximate scale. This means that if the map projection does not preserve distance then the ScaleLine control value will change as the map is panned, which is what you are experiencing. Would it be possible for you to try data that is in a map projection that does preserve distance and then test this with the ScaleLine control?

Cheers

Kerrie

MichaelErlich · ‎09-07-2011

We are currently using WGS 1984. What would you recommend as the projection? Would WGS 1984 Web Mercator be sufficient?

Correction: the tile pack is using WGS 1984 Web Mercator. That is the only one that ships with arcmap 10.1.

Anonymous User · ‎09-07-2011

Original User: psiclopz

Hi,

The ScaleBar Control has been deprecated so the recommendation is to use the ScaleLine control in the Toolkit. The ScaleLine control exhibits the same behaviour you were experiencing with the ScaleBar control because, by design the ScaleLine control takes the value at the centre of the map as the approximate scale. This means that if the map projection does not preserve distance then the ScaleLine control value will change as the map is panned, which is what you are experiencing. Would it be possible for you to try data that is in a map projection that does preserve distance and then test this with the ScaleLine control?

Cheers

Kerrie

Hi Kerrie,

If you look at the screenshots that Mike E attached, you'll see we are using the ScaleLine and not the ScaleBar.

Also, as he said, we're using WGS 1984 Web Mercator, which is the default projection for Tile Packs. Does that mean your default doesn't preserve distance?

Thanks,

James

Anonymous User · ‎09-08-2011

Original User: kscholefield

Also, as he said, we're using WGS 1984 Web Mercator, which is the default projection for Tile Packs. Does that mean your default doesn't preserve distance?

Hi James,

The WGS1984 Web Mercator Auxilliary Sphere coordinate system has gradually become the accepted default coordinate system for online maps because it provides an aesthetically pleasing global projection �?? and for people using ArcGIS Online services in conjunction with Bing map for example, then it�??s ideal. However, if you�??re concerned about correctly representing distance and area then you need to choose a coordinate system which preserves as closely as possible the attribute you�??re interested in. There are many, many projections, each designed to preserve a specific aspect of the data. See these blogs for more information and discussion on choosing the best coordinate system for your purpose:

ArcGIS Online and Web Mercator Auxilliary Sphere: http://help.arcgis.com/en/arcgisonline/content/index.html#//011q00000005000000

Measuring distance and areas when using Web Mercator Auxiliary Sphere: http://blogs.esri.com/Dev/blogs/arcgisserver/archive/2010/03/05/Measuring-distances-and-areas-when-y...

Cheers

Kerrie

JamesMcElroy · ‎09-08-2011

Gotcha. I found this in the link you provided.

Also, area and distance measurements in Mercator will not be correct since the farther north you take the measurement, the more distortion there is.

This would address then why the scale changes as you move towards Alaska in the screenshots, because you're moving farther North, correct?

Thanks,

James

Anonymous User · ‎09-08-2011

Original User: kscholefield

This would address then why the scale changes as you move towards Alaska in the screenshots, because you're moving farther North, correct?

Hi James,
That is correct - when you are moving further north towards Alaska the scale will change.

Cheers

Kerrie

MichaelErlich · ‎09-08-2011

Do you have any other configuration files available for other projections with Tile Packs? Or, are there any tools to create one, or an article that provides the details (rather than a summary of concept) that describes what the parameters mean in the xml files?

Also, it seems to me that this is not the proper way to present the scale line (just my opinion). Compare/contrast to google/bing maps. As you pan around on their maps, you will see the lengths of the scale line grow/shrink depending upon the center point of the map. This seems to be a cleaner approach than the runtime control which keeps the scaleline width the same, but changes the distance value instead. Keeping the distance label the same seems like it would be more intuitive for people that have no understanding of projections and mathematics.

Thanks,
Mike