Help with importing XY data without projection

Question

Hi, I have data that is simple local grid data (like from a total station).  When I try and import it ArcGIS (10+) wants it to have a projection or it will not seem to use correct units (Metres) for doing nearest neighbour and other geospatial tasks or add other layers.  This is just a local grid.  How can you set up data with just a grid projection as there are not options for that in projections.  I could use OSGB or UTM but that introduces other issues.  How can I work with data in a metres based grid without upsetting Projection?  Is it easy to set up a new projection that is a simple cartesan grid?  Sorry if this is a basic question but I have not had to do this in the ArcGIS10 environment and it was not an issue in earlier versions (or as I remember) .  Thanks in advance for any and all help.

DanPatterson_Retired · Answer

Yes  ... as Neil points out 'Null Island' Null Island - Wikipedia provides an additional station to which you can tie your observations into.  Its prime export is used in the tabular data industry.  It truly exemplifies null geometry as well.

NeilAyres · Answer

Well Arc is a GIS system, and it doesn't really "like" coordinates just out there floating in space.

The projection or coordinate system tells Arc what these XY numbers mean and define its relationship with a model of the earth. Where it is actually located.

So, you could set up a dummy local projection or use a standard TM, with an arbitrary central meridian, latitude of origin etc.

So if you made these both 0, 0, your data would out there floating in the gulf of Guinea, off the Nigerian coast.

JeffChartrand · Answer

Hi, thanks for the reply.  No, these are tuples being used in a local grid without real world coordinates.  Standard cartesian coordinates that you would get from a Total Station for example.  An x and y value only realitive to the local grid.

Cheers

Jeff