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#1
BillMathews

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Hello,

I'm fairly new to GIS (one class under my belt) and I'm attempting to create a map for one of my professors. Really simple map with just some point features and I'm using a shaded relief map of Idaho as the base. My problem is that I can't get the point features to project correctly on the shaded relief. The have the same projection, I've changed the projection to see if that worked (it didn't) cleared all projections and started fresh but nothing works. I do get an error occasionally saying something to the effect that some projections don't match (but they all do) which can cause some drawing errors (sorry paraphrasing can't remember exactly what the error was).

Thanks for any help,

Bill

Edited by BillMathews, 07 January 2011 - 03:00 PM.


#2
Laura Miles

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Are the projections of the data the same as the map document (I'm assuming you're using ArcGIS)? That still shouldn't cause one dataset to be off from another though. What are the steps you have been taking?
Laura

#3
dsl

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Make sure when you are changing projections you use the define projection tool to set a file's existing projection (presuming it is known), and the project tool to actually change to differing projection.

Hope that helps,
David

#4
BillMathews

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Thanks for your replies

Laura, yes I'm using ArcGIS 9.3 and the projection are the same on everything. The only steps that I have taken so far is to add my shaded relief and then bring in my point data (which was undefined). I defined the point data by importing the projection from the shaded relief. Once they didn't line up I attempted to redefine the projection on both layers but still a no go.

David, yeah I'm using the define projection tool, but I didn't know that it made a difference whether you used it or not. I will make sure that I continue to use it.

Thanks again for both of your help

Bill

#5
p-dub

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Hi Bill-

Did you receive the points as a text file? When creating point geometry from text be sure to define the Geographic Coordinate System (NAD83, NAD27, WGS84, etc...) first, then project to the desired Projected Coordinate System (State Plane, Equal Area, Conformal, etc...).

For instance, if your base map is in UTM, and your points are lat-long the import projection option won't work because the lat-long values will be applied as UTM meters.

Hope that helps.

PW

#6
BillMathews

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Hi Bill-

Did you receive the points as a text file? When creating point geometry from text be sure to define the Geographic Coordinate System (NAD83, NAD27, WGS84, etc...) first, then project to the desired Projected Coordinate System (State Plane, Equal Area, Conformal, etc...).

For instance, if your base map is in UTM, and your points are lat-long the import projection option won't work because the lat-long values will be applied as UTM meters.

Hope that helps.

PW



Hello PW,
I did receive the points in an excel table. I will give that a try and see if it works. You define the Geographic Coordinate System through the "define projection tool" or is there another way?

Thanks for your help
Bill

#7
p-dub

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Bill-

I will add my table to Arc and click the "Display xy Data". Then click on the "Edit" button under the "Edit Coordinate System". Then Choose "Select" instead of import. Navigate to Geographic Coordinate Systems and select the appropriate one. In the files I am used to, there will be a field in the table telling me to use NAD83, etc. If you do not have this info, NAD83 or WGS84 are probably good bets or ask whom ever gave you the data what the datum is. Now that the points have a datum or "Native Projection" I reproject using the ArcToolbox ->Data Management -> Projections and Transformations -> Features -> Project. Here you can use the "Import" option.

Oh yah, take a look at the lat long values. Are they Decimal Degrees or Degrees Minuntes Seconds? Or are they values in the millions and hundred thousands? This can give you a clue as to what the native projection should be.

Cheers,

PW




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