Ask A Cartographer

assigning projection to the shape file

May 14 2010 | 0 comments

Respected Sir,

Thank you so much that you replied to my question. But the solution does not solved the problem I am facing. I will try to elaborate the question.

I am using Arc Map version 9.3.
I have extracted contours from the DEM using ' Spatial analyst 'tool. Now I want to use those contours, as a line data, for further analysis. While doing measurements on shape file of the contours,
1) It is not showing proper distances and units (it is showing unknown units instead).
2) Also it is showing Y- coordinates in negative.

This could be due to some problem in projection.

i) So by right clicking on the shape file and opening " properties "I have
checked for the projection. The shape file was not showing any projection.

ii) In the same way I have checked the projection of the DEM,which was used to extract the contours,it was also not showing any projection.

So I have opened the DEM in the ERDAS 2010 software. It was showing projection as
Geographic lat-long, Datum: WGS 84. In ERDAS DEM was reprojected to UTM44N WGS 84,since the final output required is in UTM.

After re-projecting into ERDAS, the DEM in UTM coordinate system was again opened into Arc Map(with Arc info license) but it was not showing any projection. Also the same problem of negative Y-coordinates was existing. My question is,

a) Why it was not showing projection?
b) Is there any relation of false easting and false northing values with the
co-ordinates displayed in negative?
c) How to solve the problem?

To solve the problem temporarily, I have tried to assign projection to the contour's shape file
which was extracted by DEM,in Arc GIS.
the tool used was " Data Management tools " - " Projection and Transformation " -
" Define Projection "
UTM 44N WGS84.prj was assigned to the file. After running the process the observed changes were
i) It was showing UTM 44N WGS84 projection in " properties ".
ii) But the values of " extent " (Top Right Bottom Left) were as it is (with Y co-ordi. in negative). And units were shown in meters in place of " ?? "(the symbol,may be for unknown units).

d) Why it was not changing the values of extent according to the projection?
There should be some difference in the spatial co-ordinates for different projections.

{ Additional Question though it is not related with present data: The co-ordinates of the
study area are in Degree Decimals and if we want it to be displayed in meters then how to convert it? }

Also I have tried to assign some other co-ordinate system to the shape file and then convert it to the required UTM projection.The steps followed were:
i) Assigned GCS WGS84 using " define projection ".
ii) Tried to re-project it using tool " Data Management tools " -
" Projection and Transformation " - " Project " .
but still Extents were not changed,only projection viewed through " properties " was changed.

The question is

e) Do I need to mention the geographic transformation?

{ Also when the present layer is having data/shape file with one co-ordinate system
and you try to add data of some other co-ordinate system then,while opening it is asking for
Transformations. how to assign the transformation if it is not present in the list of transformations? how to create new one? is there any chart where values of dx,dy and dz are mentioned for different transformations? }

I am really thankful to you for answering to my previous questions. I know the
list of questions has increased this time...
Sorry to trouble you again, but I am stuck up with my work and help-less,since the
problem is not getting solved by the procedures which I have tried.

Thanks for giving me your precious time...
Looking forward for the solution.


Mapping Center Answer:

Because you have a number of related issues that may be causing the problem, we would like to suggest that you get directly in touch with our Technical Support Team so that they can work with you through the problem.  To help, we have provided a link from our Ask a Cartographer page. Just click on the Contact ESRI Technical Support tab and you can get to our tech team quickly and easily.

If you would like to post a comment, please login.

Contact Us | Legal | Privacy |