topic Re: What projection should I use to measure in meters? in Data Management Questions

What projection should I use to measure in meters?

CarinaZacharias — Fri, 08 Jul 2016 13:37:39 GMT

Dear all,

I want to do some distance calculations in ArcGIS, but it is always calculating in degrees. I think the only way to make it measure my distances in meters is to change the data and the data frame to an appropriate projection? (I have set the map properties to meters already.) However, I do not know which projection to choose. I am looking at an area that is roughly at 31.0309° N, 103.1831° E. I have read somewhere else that UTM is good, but Arc offers so many different UTM projections that I was lost again. I think the UTM grid should be 48.

Is anybody able to suggest a specific coordinate reference system that I can try? Thanks ever so much in advance.

Carina

Re: What projection should I use to measure in meters?

JakeSkinner — Fri, 08 Jul 2016 13:53:59 GMT

Hi Carina,

You are correct that zone 48 is what you should use. One thing that is helpful is using a utm shapefile. You will have this utm shapefile located at the following location:

C:\Program Files (x86)\ArcGIS\Desktop10.4\Reference Systems

You can add this to ArcMap and then enter in the coordinates you referenced above. Take a look at the 'Zone' field the point falls in and you will see that it's 48.

Re: What projection should I use to measure in meters?

CarinaZacharias — Fri, 08 Jul 2016 14:05:17 GMT

Hi Jake,

thanks for the answer! But what confused me was how many different UTM projections there are. If I go to projections in Arc there are many different folders under "UTM". I guess I would go for Asia, since that's where the nature reserve is located that I'm looking at. But even under Asia there are so many that have 48 in it. There is for example "Indian 1954 UTM Zone 48N" or "MONREF 1997 UTM Zone 48N" etc. ... How do I know which one to choose here?

Sorry, if this is a stupid question ...

Re: What projection should I use to measure in meters?

JayantaPoddar — Fri, 08 Jul 2016 14:16:37 GMT

If I am not wrong,

Go to Projected Coordinate System > UTM > WGS 1984 > North > 48N

Re: What projection should I use to measure in meters?

CarinaZacharias — Fri, 08 Jul 2016 14:21:53 GMT

Okay, I will try, thanks again!

Re: What projection should I use to measure in meters?

CarinaZacharias — Fri, 08 Jul 2016 14:56:32 GMT

Hi, thanks for your help. Unfortunately projecting my data to the UTM Zone 48 reference system didn't help. I also made a complete new map, set the reference system to UTM 48, imported the data - still no difference. The distance is still being calculated in degrees. And if I go to the Properties of my raster layers and to Source and look at cell size I see that these are obviously still in degrees. Do you think that could be the problem?

Does anybody have any more suggestions?

Re: What projection should I use to measure in meters?

JayantaPoddar — Fri, 08 Jul 2016 15:56:57 GMT

You should use Project Raster—Help | ArcGIS for Desktop to reproject your data from GCS to PCS. You should NOT change the spatial reference from layer properties in ArcCatalog.

Re: What projection should I use to measure in meters?

CarinaZacharias — Fri, 08 Jul 2016 16:07:23 GMT

oops, I alwys thought the "define projection" tool was the only way to change the projection. This is good to know although sadly it does still not make a difference ...

Re: What projection should I use to measure in meters?

DanPatterson_Retired — Fri, 08 Jul 2016 17:11:22 GMT

you need to open a new dataframe and add your projected data there... otherwise, the recently projected gets unprojected on-the-fly back to the coordinate system of the dataframe

Re: What projection should I use to measure in meters?

JayantaPoddar — Fri, 08 Jul 2016 18:39:29 GMT

Could you attach snapshot of the current spatial reference and extent of the layer from the layer properties?

Re: What projection should I use to measure in meters?

MelitaKennedy — Fri, 08 Jul 2016 18:49:11 GMT

Carina,

What version of ArcGIS are you using?

Based on your comment about the Define Projection tool, I am wondering whether some data layers now have incorrect coordinate systems (projections). For instance, for the rasters that have cell sizes in degrees, what coordinate system do they have? They should have a geographic one like WGS84.

Even if the layers are all using a geographic coordinate system, and the data frame is too, the measure tool should default to measuring geodesic distances and some linear unit.

Because of that, I am wondering whether data frame/layers have projected coordinate systems, but the data (coordinates) themselves are still in degrees.

Melita

Re: What projection should I use to measure in meters?

CarinaZacharias — Fri, 08 Jul 2016 20:04:43 GMT

But I did that ...

Re: What projection should I use to measure in meters?

CarinaZacharias — Fri, 08 Jul 2016 20:08:47 GMT

I am using ArcMap 10. All the rasters are now in UTM North 48. I can provide screen shots on Sunday or Monday of the properties of the layers.

@Melita: I didn't know that was possible - that the data frame and layers could have projected coordinate systems, but the coordinates could still be in degrees. What would I do then to solve this?

Re: What projection should I use to measure in meters?

CarinaZacharias — Mon, 11 Jul 2016 08:07:01 GMT

Here are two screen shots:

Re: What projection should I use to measure in meters?

JayantaPoddar — Mon, 11 Jul 2016 08:43:03 GMT

Thank you for the screenshots....

It seems that the coordinate values correspond to the values in Decimal Degrees (GCS). You need to do two steps.

1. Using Define Projection, define a Geographic coordinate system (GCS_WGS_1984).

This will ensure that the coordinate values corresponds to its correct spatial reference.

2. Next, using Project Raster, you can reproject the above raster from Geographic CS to Projected CS (WGS_1984_UTM_Zone_48N)

Re: What projection should I use to measure in meters?

CarinaZacharias — Mon, 11 Jul 2016 09:04:38 GMT

Okay! And do I need to start a new map for this or should I try it in the old one?

Re: What projection should I use to measure in meters?

JayantaPoddar — Mon, 11 Jul 2016 09:09:19 GMT

Open it in a new map so that the spatial reference of the data frame gets reset.

Re: What projection should I use to measure in meters?

CarinaZacharias — Mon, 11 Jul 2016 09:11:39 GMT

So, just to make sure I do everything right this time: I define projection and reproject raster in my old map. And then I open the data in a new map, but without defining a reference system for the data frame. And then it should (in theory) work?

Re: What projection should I use to measure in meters?

JayantaPoddar — Mon, 11 Jul 2016 09:14:16 GMT

Yes. When we open a layer in a new map, the data frame takes up the coordinate system of the added layer.

Re: What projection should I use to measure in meters?

CarinaZacharias — Mon, 11 Jul 2016 09:27:03 GMT

Hmm, after doing this and open them in a new map they are displayed slighlty askew (see below). But I will try the tool that involves the distance calculation anyway and see if it works ...