How do I change (the size of) the underlying planet for measurements?

[JanetCarson]

I am a high school teacher with a brand-new ConnectED K-12 account for ArcGIS Online and am trying to figure out the very basics to use this for planetary exploration.

I have loaded maps of Mars, but my measurements are as if the lat/longs were on Earth.

What I've done so far:

Loaded the maps

• basemap: ArcGIS Server - Mars MDIM2.1 Basemap
• layers: ArcGIS Server - Mars Global GIS Overlay Service

both of these servers are from thare_USGS

When I turn on the measurement tool, the widths of common features (e.g. Olympus Mons) are about twice what you'd expect (checked vs JMARS), as if the lat/longs were on Earth rather than Mars.

How do I change (the size of) the underlying planet for measurements?

[DarrenWiens2]

I've never worked with Mars data, but I suspect you need to change your data frame coordinate system to one of the Mars CRSes (e.g. Mars 2000 or Mars 1979), if you haven't done so already. These are both geographic, so they will report units of degrees. I do not see any projected CRS for Mars, at least not packaged by default in ArcGIS 10.2.2.

[JanetCarson]

Sorry, but very new to this: what is a CRS?

[DarrenWiens2]

CRS = Coordinate Reference System. I just noticed that you're using ArcGIS Online, which I don't use. The process in ArcGIS Desktop would be to switch the CRS in the data frame properties, but I'm not sure how to do that in AGOL.

[JanetCarson]

Sorry, but very new to this: what is a CRS?

[RandyBurton]

This sounds like an interesting project.  I don't know how you can change the settings in ArcGIS Online.  Since AGOL is using the size of the earth, you might need to use a scale factor of about 53% to calculate the actual distance on Mars.

[ChrisDonohue__GISP]

Adding Melita Kennedy (ESRI coodinate system expert) to this thread, as she might have insight on this.

Chris Donohue, GISP

[RandyBurton]

It seems ArcGIS Online cannot properly measure Mars coordinates (using the Mars 2000 projection).  If you view your map using the Explorer for ArcGIS app, it will give better measurements. Online measured Olympus Mons at about 650 miles across; Explorer gave a measurement of about 335 miles across.