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#1
Asli

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Hi everyone,

My name is Asli,I am from Norway.I am an IT student,but doing my thesis in GIS analysis. My question is, i have two shape files from different sources.When i open them separately in arcmap they both work fine ,but when i try to open them together as different layers on the same page, only the first one i open is visible.I check there projection and make it the same.

I am new to GIS. Please help me how i can fix this.By the way i am using ArcGIS 9.3.

#2
Sv_BG

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How exactly did you "make" their projection the same? Did you transform one of the shapefile's projection, to fit the other shapefile, by the project tool from the arctoolbox, or just changed it (simply selected another one)? I think that might be the problem. Try to reproject the shapefile using the tool form the arctoolbox.

In fact I think both of the layers are visible (you can see them in Arcmap), but they are not projected at the same place. Try to zoom to each of the layers (right click and zoom to layer) and probably you will be able to see them.

Some info from the available arcgis help :

Coordinate systems and data frames
To display your data correctly, a data frame uses a coordinate system. This can be any coordinate system ArcGIS supports. The data frame's coordinate system need not be the same as the data you are using, although if ArcMap has to project your data on the fly, it does take longer to draw.

When ArcMap is started with a new, empty map, the coordinate system for the default data frame is not defined. When you add data with a defined coordinate system, ArcMap will automatically set the data frame's projection to be the same as that of the data. The first layer added to an empty data frame sets the coordinate system for the data frame, but you can change it if necessary. If the first layer does not have a coordinate system, ArcMap will set the coordinate system to Unknown.

As you add subsequent layers, they are automatically transformed to the data frame's coordinate system as long as there's enough information associated with the layer's data source to determine its current coordinate system. If there isn't enough information, ArcMap will be unable to align the data and display it correctly. In this case, you'll have to supply the necessary coordinate system information yourself.


You can read the full article here - http://webhelp.esri....ordinate_system

p.p. can you upload the files somewhere and send me a link?

Hope that helps!

Good luck,
Svetoslav

Edited by Sv_BG, 09 December 2009 - 01:01 AM.


#3
jmcandrew

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You may want to use a program like uDig to do the reprojection, it's quick, efficient, and free!

#4
Fran├žois Goulet

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Like Svetoslav said, I thing the error is that they could be in the same coordinate system when they shouldn't be.

One common mistake is with the "Define Projection". Let say you have one in lat-long and the other in UTM.

In the first one, the coordinates will be something like (-52.6, 45.3) and the other (233000, 5450000). If you want to display both of them in UTM (Arc will project them on-the-fly, but if the projection information are missing) and you "define" the projection of the first one as UTM (because you want to project it in UTM), the coordinates will become -52.6 meters East and 45.3 meters north. The "Define Projection" will simply assign a projection the the shapefile without changing its coordinates. But, if you define the projection of the first one as lat-long and then project it in UTM, then, the coordinates of the points, vertices, ... in it, will be "translated" into UTM and then, they will display correctly.

I've seen this many times and still happens to me when I'm playing with data from different sources.

#5
frax

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Zoom in to one of the layers, and look at the coordinates in the status bar. Then zoom in to the other layer and look at the coordinates in the status bar. Probably one of them is way off.

jmcandrew - I don't think it is very helpful to bring up uDig in an ArcGIS specific question...
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#6
Asli

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Thank you all for you suggestions. I have been trying to do almost all the things you suggested , so far the only thing which work for me is zoom to layer. I can see both the data when i do zoom to layer. I tried to project it using define project tool from the arctoolbox and make them the same, but i am still struggling. I will try to find a way to upload the data some where so you can see it.

Thank you.

#7
Sv_BG

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I guess you misunderstood something. You shouldn't use the "Define projection tool", but the "Project" tool. These are two different tools. You need the second one, which is located in:

ArcToolbox --> Data Management tools --> Projections and Transformations --> Feature --> Project

Good luck,
Svetoslav

#8
DaveB

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OK, let's back up here a little - if the 2 data layers are not lining up but they should then one or both do not have proper coordinate system information. Without thta I'm not aware of any software than will make them match up.

The Define Projection tool allows you to define the actual current coordinate system of the data. If you don't have the data's current coordinate system defined correctly or if there is no coordinate system info attached to the data it cannot be projected to another coordinate system correctly.
If you know what the correct coordinate system is you can use the Define Proejection tool to set that. If you don't know what it is and you can get the information from the data provider that's usually the best and easiest way to go.

Otherswise you'll have to experiment to discover the correct coordinate system. That can be tricky for a "newbie". If anyone is in that boat and working with ArcGIS I would recommend posting on the ArcGIS Desktop User Forums. You'll likely get some help from Melita Kennedy, a fellow ESRI employee and one of the most knowledgeable and helpful people I know when it comes to projections/coordinate systems.

Once you have the 2 data layers setup with their correct current coordinate systems they should line up in ArcMap. If they don't something is either defined incorrectly or the data has been shifted from its correct location. If they do line up correctly then you can proceed with reprojecting.

Here's a useful article about figuring out an unknown coordinate system:
How to identify an unknown projected coordinate system using ArcMap
You can find a lot more inofrmation about coordinate systems if you search ESRI Support Center for "coordinate sytem".
Dave Barnes
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#9
Melita Kennedy

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DaveB has a lot of good the suggestions. While you can post the data (here) or on the ArcGIS forum, you can try telling us the data extents for both layers. You should be able to get this information in ArcCatalog. Select one of the datasets, click the metadata "tab" and go to the Spatial section. To help figure out which dataset is 'bad', please provide the following information:

1. current coordinate system
2. projected/local extents - in the metadata, that's the 'native' coordinates
3. decimal degree extents - one of the layers will wildly incorrect values. That's the one with a wrong coordinate system.
4. what location the data represents - city, county, lake - something that can be identified on another map/atlas

Melita

#10
jbl

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I guess you misunderstood something. You shouldn't use the "Define projection tool", but the "Project" tool. These are two different tools. You need the second one, which is located in:

ArcToolbox --> Data Management tools --> Projections and Transformations --> Feature --> Project

Good luck,
Svetoslav



I noticed this and thought it might simplify re0projecting a shp layer. In the past I just opened a new blank workspace, set the new projection that I want in the Data Frame properties (ie...NAD83). Census Tiger 2000 are WGS84, so I add the WGS84 shp file then export as a new layer with the coordinate syatem of the Data Frame (NAD83)

When I try this method (ArcToolBox..Feature..Project) on the same files I get an error message "Undefined geographic transformation"

jbl

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#11
Melita Kennedy

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I guess you misunderstood something. You shouldn't use the "Define projection tool", but the "Project" tool. These are two different tools. You need the second one, which is located in:

ArcToolbox --> Data Management tools --> Projections and Transformations --> Feature --> Project

Good luck,
Svetoslav



I noticed this and thought it might simplify re0projecting a shp layer. In the past I just opened a new blank workspace, set the new projection that I want in the Data Frame properties (ie...NAD83). Census Tiger 2000 are WGS84, so I add the WGS84 shp file then export as a new layer with the coordinate syatem of the Data Frame (NAD83)

When I try this method (ArcToolBox..Feature..Project) on the same files I get an error message "Undefined geographic transformation"

jbl


Hi,

That's correct. NAD 1983 != WGS 1984, and the Project tools require a transformation if the geographic coordinate systems (datums) are different. Because its Census data, and from 2000, I would just use NAD_1983_To_WGS_1984_1 which has zeroes for the transformation parameters. On a side note, I'm surprised the Census data is using WGS84. It should be NAD83 already, or maybe NAD27. When *did* the Census switch their data to NAD83?

Melita




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