point distance/near analysis units?

Question

hi all, have been learning lots here, will have more Qs for sure too...

I'm running both point_distance and generate_near_table on a couple of point layers.  I often specify a search radius of say 1 or 3km, which is easily set, and sometimes I don't set a search radius and take everything back I can get.  either way, the distance columns in the resultant dbfs are in what I think decimal degrees distance; how can I get back a km distance value?  I don't see an option in either dialogue for specifying units, but, I'm a bit new to this.

thanks very much,

cj

ChrisJ · Answer

thanks for your help eric; after a bit of clicking I've gotten the measurements the way I want now...

thanks again,

cj

EricRice · Answer

CJ,

ArcMap's dataframe (right click 'layers' > properties in the TOC)  does not have to be the same coordinate system as the data in the map (the two point layers).  When you add GCS points to a map defined in UTM space the application projects the data on the fly to UTM.  This is very common in ArcGIS. A single UTM zone isn't suitable for data that covers all of Canada so I'm not sure why the dataframe is set to that rather than something more continental.

For your analysis though, the dataframe coordinate system is irrelevant.  Your data is GCS and that is what the tools are going to use.  So, you must run the Project tool.  The tools is pretty basic.  Give it your input, select an output coordinate system suitable for Canada and distance analysis, define the output name/location, and set any geographic transformations if you're going to be switching datums.  Transformations are only optional if you're not switching datums.

Eric

ChrisJ · Answer

thanks for the info eric.  I can't emphasize enough how much of a novice I am with arc, after having come from a long mapinfo background, so if anyone's up for it I could still use more clarification....

- my two point layers, when put into a 'generate near table' are coming back with what I presume are decimal degrees for the DISTANCE column; I would prefer metres.
- point layer 1 ('stores'), under its source is set to geographic coordinate system: GCS_NAD_1983_NSRS2007 and datum: D_NAD_1983_NSRS2007.  it was generated using lat and long columns in the original table to 'add XY data'.
- point layer 2 ('competitors'), under its source is set to geographic coordinate system: GCS_NAD_1983_NSRS2007 and datum: D_NAD_1983_NSRS2007. it was also generated using lat and long columns from the original table to 'add XY data'.
- if I right-click the 'layers' at the very top of the ToC, and go to the coordinate system tab, it shows:

WGS_1984_UTM_Zone_17N
Projection: Transverse_Mercator
False_Easting: 500000.000000
False_Northing: 0.000000
Central_Meridian: -81.000000
Scale_Factor: 0.999600
Latitude_Of_Origin: 0.000000
Linear Unit: Meter

so, I see a mismatch here in that the layers themselves are geographic (GCS_NAD_1983_NSRS2007?) but the 'layers' shows projected (UTM zone 17N)?  is one taking precedence over the other, resulting in a decimal degrees measurement for DISTANCE in the near table?  is there some blatant mismatch here that I should address first, and how?  if something such as the project tool in the toolbox is what I'll need, some step by step instructions would be very handy.  my goal is to have these two point layers on a properly projected map of all of canada (not just one UTM zone), which comes back with metres when I generate a near table...

thanks very much all,

cj