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Getting Technical

How to change the projection in ArcGIS Online in one easy step

ArcGIS Online is a convenient online mapping tool that allows users to combine thematic data with a number of ready-made basemaps. For those living in the far north, however, all of this convenience is lost simply because the projection that's used (Web Mercator Auxiliary) really distorts their area of interest. Compare the map of Inuvik (latitude 68 north) in Web Mercator Auxiliary (Figure 1) to one that's in a more appropriate Lambert Conformal Conic projection (Figure 2). Both are roughly the same scale (around 1:145,000), but keep in mind that the orientation of the maps differ.

Figure 1: Inuvik, Northwest Territories at 68 degrees north in Web Mercator auxiliary projection

Figure 2: Inuvik, Northwest Territories in Lambert Conformal Conic projection. North is about 38 degrees clockwise from the top.

You may not know this but the ArcGIS Online viewer can also display maps in projections other than the standard Web Mercator Auxiliary. You might be surprised to learn that you can do this in one easy step.

When adding a data layer with the desired projection to your map in ArcGIS Online, select the option to use it as a basemap. This will cause the viewer to select the projection parameters associated with the layer and display the map in your chosen projection.

Figure 3: Setting the projection by using the projected layer as the basemap

You can then pan and zoom about your map as you normally would. Keep in mind that any additional layers added will be re-projected on the fly to match the projection you’ve chosen. To minimize your browser's workload, you should ensure that any additional layers are in the same projection. Keep in mind that re-projecting cache will result in a degradation of map quality and display speed and may cause your browser to crash.

Figure 4: A Lambert Conformal Conic projected map in the ArcGIS Online viewer

See this map in the Lambert Conformal Conic projection, produced by Natural Resources Canada, viewable on ArcGIS Online.

Paul
Heersink
Production Manager, Community Maps
Paul Heersink is a cartographer and Production Manager of Esri Canada’s Community Maps Program: an initiative that is aiming to build a seamless topographic basemap using contributor data. He has over 15 years of cartographic experience, working in both the public and private sectors. Paul has always been interested in mapping and drew his own atlas at the age of 10. He took a detour in his career through the fields of psychology and social work before returning to cartography.

Comments

I agree that Mercator is a poor projection for high latitudes but LLC has issues with rotation around the central meridian when then viewing area is nit near the central meridian. Why hasn't the web world started using a projection that reduces the distortion at high latitudes like a Gall or Miller projection? Not only is the North not stretched, areas of the map away from the central meridian are not rotated so North is always up.
After all, aren't we the map people, can't we do it better that Google?

James - you raise a legitimate concern with today's access to multiple technologies and projections. Essentially the Web Mercator Auxiliary projection by Esri because it has become the standard web projection. It has become the standard for a number of reasons: it is easily calculated, it is suitable for large scale maps for most of the world (at least the populated parts), and the directions are same regardless of what part of the map you are looking at (i.e. north is always to the top). When projecting from an ellipsoid to a flat surface, any projection is going to have its shortcomings and this is the case with Web Mercator and with the Gall and Miller projections. For a more detailed discussion on why Web Mercator was chosen as the standard web projection, refer to http://www.mapthematics.com/forums/viewtopic.php?f=8&t=251.

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