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GIS Help Clinic

1356710

Comments

  • Registered Users Posts: 3,803 El Siglo


    I can't believe I'm after getting this far to begin with, I spent a good six hours practicing Arc 9.2 yesterday and spent the last 2 hours working on this map (below). I'm quite proud of it as this is my first ever map in ArcGIS! Only problem is, I've done everything by the steps outlined it's jus that there's these white polygons that don't seem to have a land use, I've added in absolutely everything and to no avail can I figure out why these won't colour properly. Any help would be appreciated!:D

    picture.php?albumid=729&pictureid=6800


  • Closed Accounts Posts: 85 ✭✭✭ YoureATowel


    El Siglo wrote: »
    I can't believe I'm after getting this far to begin with, I spent a good six hours practicing Arc 9.2 yesterday and spent the last 2 hours working on this map (below). I'm quite proud of it as this is my first ever map in ArcGIS! Only problem is, I've done everything by the steps outlined it's jus that there's these white polygons that don't seem to have a land use, I've added in absolutely everything and to no avail can I figure out why these won't colour properly. Any help would be appreciated!:D

    picture.php?albumid=729&pictureid=6800

    I can't see your image but I'd wager that it's as simple as having a missing layer. Go to View-Layout View. Now go to View-Data Frame Properties. Select the Frame tab.

    For Background click the Style Selector button. Select Properties and then for Fill Color select a bright, standout colour that you have not yet used on the map. Bright Red for example. Click OK until the map redraws. You have in effect changed the virtual sheet of paper on which the map is drawn from white to red.

    Have these mysterious white polygons changed colour to bright red? If they have it means a layer is missing and the white areas were in fact holes in the coverage of the data.


  • Registered Users Posts: 3,803 El Siglo


    I can't see your image but I'd wager that it's as simple as having a missing layer. Go to View-Layout View. Now go to View-Data Frame Properties. Select the Frame tab.

    For Background click the Style Selector button. Select Properties and then for Fill Color select a bright, standout colour that you have not yet used on the map. Bright Red for example. Click OK until the map redraws. You have in effect changed the virtual sheet of paper on which the map is drawn from white to red.

    Have these mysterious white polygons changed colour to bright red? If they have it means a layer is missing and the white areas were in fact holes in the coverage of the data.

    The image is coming up on my computer now (windows 7) but not on the older college computer (xp).

    Cheers in any case!:D


  • Closed Accounts Posts: 74 ✭✭✭ lil*lady


    I'm kind of still having a problem with my polygons. I want to get them really precise - but when I do them (See A in the attachment) they come out weird (See B).

    I've tried to edit them, but...it always goes back to the last point where I stopped digitising at, I can't seem to go to any other point on the polygon, or get to put in a pont on a line.

    Would it be better using lines and then transforming them into a polygon? Also I've heard about a "topology" tab... would that be any use? The shapes I want to make are more rounded (like this for example) then the square shapes I'm getting currently.

    Again, pretty clueless, but any help would be greatly appreciated.


  • Closed Accounts Posts: 85 ✭✭✭ YoureATowel


    lil*lady wrote: »
    I'm kind of still having a problem with my polygons. I want to get them really precise - but when I do them (See A in the attachment) they come out weird (See B).

    I've tried to edit them, but...it always goes back to the last point where I stopped digitising at, I can't seem to go to any other point on the polygon, or get to put in a pont on a line.

    Would it be better using lines and then transforming them into a polygon? Also I've heard about a "topology" tab... would that be any use? The shapes I want to make are more rounded (like this for example) then the square shapes I'm getting currently.

    Again, pretty clueless, but any help would be greatly appreciated.


    Looks like issues with the XY Tolerance of the polygon feature class. Is it contained within a Geodatabase? Is it in a projected or geographic coordinate system?

    The XY Tolerance is often referred to as the Cluster Tolerance meaning that points that are within this distance of each other are clustered/merged together.

    A dataset in a projected coord system has a default XY Tolerance of 0.001 METERS. I would guess that this polygon is in a geographic coordinate system and has mistakenly been given an XY Tolerance of 0.001 DEGREES instead of something like 0.00000001. The result would be that points that are digitised 100 meters apart are within the tolerance and are merged into a single point.

    That would be my guess so check the XY Tolerance.


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  • Registered Users Posts: 3,803 El Siglo


    Cheers YoureATowel, just did those steps and it turns out you were right.
    Here's the map now:
    picture.php?albumid=729&pictureid=6808

    Is there anyway to figure out what the missing layer was? I've tried inputting in nearly every layer and it's driving me mad.


  • Registered Users Posts: 3,803 El Siglo


    Actually, I just figured it out, I was missing a "sports and leisure facilities" layer... Seriously, who builds a football pitch at the end of a runway?:D

    Thanks a million for everything YoureATowel!


  • Closed Accounts Posts: 85 ✭✭✭ YoureATowel


    El Siglo wrote: »
    Cheers YoureATowel, just did those steps and it turns out you were right.
    Here's the map now:
    picture.php?albumid=729&pictureid=6808

    Is there anyway to figure out what the missing layer was? I've tried inputting in nearly every layer and it's driving me mad.


    Just repeating all the steps again won't help you to learn anything new so try this. This method would take me a couple of seconds to deduce what layer is missing.

    1. Go to ArcToolbox-Data Management Tools-General-Merge. For input Datasets add all the Corine layers you have on the map. Choose an appropriate name, say AllData.shp, and a location for the output. Click OK. As you have dramatically reduced file sizes from the original this will only take a few seconds.

    2. Add to ArcMap and open the table. Right click on the field Code and select Summarize. Call the output SumCode.dbf and add the resulting table to the map. This table will give you a count of every different Code value in the AllData.shp shapefile. Therefore, any Code value missing from this file will also be missing from your map.

    3. You can now join SumCode.dbf to the table JoinData you made before. Right click on JoinData.dbf in the Table of Contents, select Joins and Relates-Joins.

    4. For 1 choose Join. For 2 choose SumCode. For 3 choose Code. For Join Options make sure Keep All Records is selected. Click OK.

    5. The field Count_Code is now added to JoinData. As JoinData contains all Corine layers if Code_Count in this table has no value, ie <null>, then the corresponding layer is not included on your map.

    6. By inspection it's obvious that some of these have no relation to Ireland, eg Vineyards. the rest give you a significantly reduced number of layers to check.


    El Siglo wrote: »
    Actually, I just figured it out, I was missing a "sports and leisure facilities" layer... Seriously, who builds a football pitch at the end of a runway?


    Thanks a million for everything YoureATowel!

    Hadn't seen that.


  • Registered Users Posts: 3,803 El Siglo


    I came across this website there now, needless to say it's the shit!
    http://www.diva-gis.org/gData


  • Registered Users Posts: 3,803 El Siglo


    I just downloaded the Irish roads network from there, added it to a project and it seems to be minuscule compared to the rest of my layers. You having any issues with it?

    Not with the data from that website, I just downloaded the administrative divisions (counties) nothing much else really. They don't have a lot of layer, but I'm working with corine data from the EEA and I just overlay the administrative division layers with my corine stuff and it seems to work okay. I'm pretty new to all of this but here's what I've managed to get done in the last two days or so:
    here's the one using that website shapefiles, and here's one using the EEA shapefiles.

    I am really having trouble uploading X and Y coordinates, it won't work on my Arc 9.2, I'll try it again tomorrow and see if it works again.


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  • Registered Users Posts: 6,032 ✭✭✭ Rowley Birkin QC


    El Siglo wrote: »
    Not with the data from that website, I just downloaded the administrative divisions (counties) nothing much else really. They don't have a lot of layer, but I'm working with corine data from the EEA and I just overlay the administrative division layers with my corine stuff and it seems to work okay. I'm pretty new to all of this but here's what I've managed to get done in the last two days or so:
    here's the one using that website shapefiles, and here's one using the EEA shapefiles.

    I am really having trouble uploading X and Y coordinates, it won't work on my Arc 9.2, I'll try it again tomorrow and see if it works again.

    I seemed to get around the size problem okay but I'm having trouble getting them to project to ITM now even following Youreatowels guide. I'll try again in the morning. Handy resource though.

    Did you try using any of the elevations?


  • Closed Accounts Posts: 85 ✭✭✭ YoureATowel


    I just downloaded the Irish roads network from there, added it to a project and it seems to be minuscule compared to the rest of my layers. You having any issues with it?

    Go to View-Data Frame Properties. Under Current coordinate system does it say Unknown?

    When you start a new map the data frame is given no projection by default. However, this is then automatically set to the coordinate system of the FIRST layer added to the map. If you later add layers that are in a different coordinate system ArcMap can project this data to display it in the data frame.

    Example 1
    1. Add layer in Irish National Grid. Data Frame coordinate system set to ING.

    2. Add layer in WGS84. ArcMap projects this layer "on-the-fly" so it can be viewed in the Data Frame, ie it's projected to ING.

    3. Add layer with no projection. ArcMap cannot reproject this layer as it doesn't know its coordinate system. ArcMap will assume that it's in the same coordinate system as the data frame. In this case if the layer is in ING there won't be a problem. However, if it's actually WGS84 then ArcMap will make the mistaken assumption that a point at -8.5 ,53.5 is in meters on Irish National Grid rather than degrees.

    However, this is not the case here as the IRL_Roads shapefile I downloaded has a prj file associated. It is in WGS84. So I would imagine this is what you did.

    Example 2
    1. Added layer with unknown coordinate system. Data Frame coordinate system set to Unknown.

    2. Added layer in Irish National Grid. ArcMap adds the layer. There are no apparent problems as the first, unknown file was actually in ING but this was not known. They overlay perfectly.

    3. Added layer in WGS84. ArcMap adds the layer but cannot reproject it. The result is that a degree is assumed to be a meter and you saw the result.


  • Closed Accounts Posts: 85 ✭✭✭ YoureATowel


    El Siglo wrote: »
    I am really having trouble uploading X and Y coordinates, it won't work on my Arc 9.2

    What input file type are you using? A common problem associated with trying to use Display XY Data with DBF files is that the coordinate values are held in fields that are of type Text rather than one of the numeric types.

    For Display XY Data to work the X and Y fields in the DBF must be numeric.


  • Registered Users Posts: 6,032 ✭✭✭ Rowley Birkin QC


    Go to View-Data Frame Properties. Under Current coordinate system does it say Unknown?

    When you start a new map the data frame is given no projection by default. However, this is then automatically set to the coordinate system of the FIRST layer added to the map. If you later add layers that are in a different coordinate system ArcMap can project this data to display it in the data frame.

    Example 1
    1. Add layer in Irish National Grid. Data Frame coordinate system set to ING.

    2. Add layer in WGS84. ArcMap projects this layer "on-the-fly" so it can be viewed in the Data Frame, ie it's projected to ING.

    3. Add layer with no projection. ArcMap cannot reproject this layer as it doesn't know its coordinate system. ArcMap will assume that it's in the same coordinate system as the data frame. In this case if the layer is in ING there won't be a problem. However, if it's actually WGS84 then ArcMap will make the mistaken assumption that a point at -8.5 ,53.5 is in meters on Irish National Grid rather than degrees.

    However, this is not the case here as the IRL_Roads shapefile I downloaded has a prj file associated. It is in WGS84. So I would imagine this is what you did.

    Example 2
    1. Added layer with unknown coordinate system. Data Frame coordinate system set to Unknown.

    2. Added layer in Irish National Grid. ArcMap adds the layer. There are no apparent problems as the first, unknown file was actually in ING but this was not known. They overlay perfectly.

    3. Added layer in WGS84. ArcMap adds the layer but cannot reproject it. The result is that a degree is assumed to be a meter and you saw the result.

    Cheers for replying so late YAT.

    Under current coordinate system I have IRENET 95. I've added quite a few layers to it now, all using your method for "altering" the projection from WGS 84 or ING to ITM and they have all lined up perfectly. Just running into a stumbling block with these ones. Any other issues that might be causing this?

    Thanks again for all the help on thread, you are an invaluable resource!


  • Closed Accounts Posts: 85 ✭✭✭ YoureATowel


    Cheers for replying so late YAT.

    Under current coordinate system I have IRENET 95. I've added quite a few layers to it now, all using your method for "altering" the projection from WGS 84 or ING to ITM and they have all lined up perfectly. Just running into a stumbling block with these ones. Any other issues that might be causing this?

    Thanks again for all the help on thread, you are an invaluable resource!

    Is your problem that you can't project the diva-gis.org data from WGS-84 to ITM. The process is
    Use ArcToolbox-Data Management Tools-Projections And Transformations-Feature-Project to change the coordinate system from WGS84 to ITM. For Output Coordinate System go to Coordinate Systems\Projected Coordinate Systems\National Grids and select IRENET95 Irish Transverse Mercator.prj. For Geographic Transformation use IRENET95_To_WGS_1984_1.

    Even if you add the original WGS84 diva-gis.org data to a Data Frame that has a Current coordinate system set to IRENET95_Irish_Transverse_Mercator, ArcMap will automatically carry out the projection "on-the-fly" and the WGS84 data will overlay correctly with the ITM data.


  • Closed Accounts Posts: 85 ✭✭✭ YoureATowel


    Did you try using any of the elevations?

    It's important to note that unlike the shapefiles, the elevation data from diva-gis.org isn't in ArcGIS compatible format. It's actually in IDRISI grid format.

    1. Install the DIVA-GIS application on your PC.
    2. Add the IRL_alt.grd file as a layer to the DIVA-GIS data frame.
    3. Data-Export Gridfile-Single File.
    4. For File Type choose ESRI ASCII. Also select an appropriate output location and name. Press Apply.
    5. Now open ArcMap with A New Empty Map. Add your newly exported ASCII elevation file.
    6. When added it looks decidedly unimpressive as the display symbology settings are incorrect.
    7. Right click on the layer, select Properties and then open the Symbology tab. Under Show change from Stretched to Classified.
    8. Right click on the Color Ramp, ie the strip that gradually changes from black to white, and uncheck Graphic View. Select Color Ramp "Elevation #1".
    9. Continue to increase the number of classes and press apply until you are satisfied.

    Alternatively, to recreate the style used in DIVA-GIS, you can press Classify, set Classes to 5 then set Method to Manual. Under Break Values place 168, 343, 518, 693, 868 in that order. Change to the appropriate colour style for each class.


  • Registered Users Posts: 6,032 ✭✭✭ Rowley Birkin QC


    Is your problem that you can't project the diva-gis.org data from WGS-84 to ITM. The process is


    Even if you add the original WGS84 diva-gis.org data to a Data Frame that has a Current coordinate system set to IRENET95_Irish_Transverse_Mercator, ArcMap will automatically carry out the projection "on-the-fly" and the WGS84 data will overlay correctly with the ITM data.

    Have tried again using what you outlined here and still having issues getting it to line up with my other layers projected in ITM 95. Is there anything else I could be missing?

    I've checked all other layers in the project and they are in ITM 95. Following the ArcToolbox procedure you listed the DIVA shapefiles are also shown as ITM95 but when I add them to the project they are way off as if still projected in WGS_84.

    Thanks again.


  • Registered Users Posts: 3,803 El Siglo


    What input file type are you using? A common problem associated with trying to use Display XY Data with DBF files is that the coordinate values are held in fields that are of type Text rather than one of the numeric types.

    For Display XY Data to work the X and Y fields in the DBF must be numeric.

    Thanks for that YoureATowel.:D

    Here's what I'm after doing.

    Here's what my excel spread sheet looks like.

    Here's what the .txt (tab delimited) file looks like.

    Here's what things look like when I upload them to ArcMap.

    The data is uploaded but doesn't appear on my sites. I know the area that I'm looking at with regards my gps points but they still don't appear.


  • Closed Accounts Posts: 74 ✭✭✭ lil*lady


    Looks like issues with the XY Tolerance of the polygon feature class. Is it contained within a Geodatabase? Is it in a projected or geographic coordinate system?

    A dataset in a projected coord system has a default XY Tolerance of 0.001 METERS. I would guess that this polygon is in a geographic coordinate system and has mistakenly been given an XY Tolerance of 0.001 DEGREES instead of something like 0.00000001. The result would be that points that are digitised 100 meters apart are within the tolerance and are merged into a single point.

    That would be my guess so check the XY Tolerance.

    Thanks YourATowel, it wasn't in a geodatabase but I've since done up a geodatabase with a polygon for the lake. I've set the coordinate system to the projected Irish Grid 65, and tried doing it in geographic coordinates of TM65 (My other data is in GCSTM65_Transverse_Mercator I've no Z coordinate system, does that affect it?) and given it the XY Tolerance you recommended however I'm still having the same problems as it won't recognise the geometry. :( Any ideas what I'm doing wrong? Can't really start making my map until I've got this down, so any help would be appreciated.

    Also just realised that I probably should put everything else into a database. Again, fairly clueless, but with a supervisor who doesn't show up and no-one in uni to help with showing me the basics you've pretty much been invaluable as RBQC said, so once again thank you very much! Back to the drawing board I guess. Arg.


  • Registered Users Posts: 3,803 El Siglo


    I've figured out why my coordinates aren't coming up, they're GPS points in northings and westings and I haven't converted them to the Irish National Grid. I've tried doing it on the OSi website through a batch conversion, I've tried downloading a package from the OSi which is supposed to do it and I've tried doing it with individual points on the OSi website, still to no avail. Anybody got any suggestions?


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  • Registered Users Posts: 6,032 ✭✭✭ Rowley Birkin QC


    Still having issues getting the DIVA roads layers to line up with my other layers.

    Just noticed this morning that the extent (General > Source) of the DIVA roads layer, having been projected to IRENET 95 ITM, is vastly different to the existing IRENET 95 ITM layers in my existing project.

    Existing layers:
    TOP: 459743.199900 m
    LEFT: 30161.660100 m
    RIGHT: 334528.400100m
    BOTTOM: 19703.940000 m

    DIVA Roads Layer (From WGS_84 to IRENET 95 ITM)
    TOP: 949553.281667 m
    LEFT: 431169.024752 m
    RIGHT: 728108.469048 m
    BOTTOM: 525182.475228 m

    attachment.php?attachmentid=120459&stc=1&d=1279279096
    Is there any way to manually change the extent to get the layers to sit on top of each other? I can't see what else I'm doing wrong, apologies if it's blindingly obvious!


  • Closed Accounts Posts: 74 ✭✭✭ lil*lady


    Ok, decided to cut my losses and start from scratch, and it's working so far. Hurray. Thanks again!
    El siglo, I'd a quick look online and you can find converters to UTM...would that be any use to you? And then again I don't know, but there might be a way to import them into ArcMap with changing the coordinates the way YAT was saying before - I could be well off now, but just an idea...


  • Closed Accounts Posts: 85 ✭✭✭ YoureATowel


    El Siglo wrote: »
    I've figured out why my coordinates aren't coming up, they're GPS points in northings and westings and I haven't converted them to the Irish National Grid. I've tried doing it on the OSi website through a batch conversion, I've tried downloading a package from the OSi which is supposed to do it and I've tried doing it with individual points on the OSi website, still to no avail. Anybody got any suggestions?

    Usually if I was faced with this problem I would write a python script that would convert the data to a workable format. Here, as there are only a couple of points, you can do it manually.

    1. Open the data in Excel as you have shown

    2. In Cell D1 type "Long Degrees"

    3. In Cell E1 type "Long Minutes"

    4. in Cell F1 type "Lat Degrees"

    5. In Cell G1 type "Lat Minutes"

    6. In Cell H1 type "LONG"

    7. In Cell J1 type "LAT"

    8. Place in cursor in Cell D2, type "=LEFT(B2,2)". Press return and the cell value will change to 52, ie the full degree value of the "Northing" cell. Select the cell again and fill down to insert the data for the entire column.

    9. Place in cursor in Cell E2, type "=MID(B2,3,LEN(B2)-2)". Press return and the cell value will change to 43.246, ie the minute value of the "Northing" cell. Select the cell again and fill down to insert the data for the entire column.

    10 Place in cursor in Cell F2, type "=LEFT(C2,1)". Press return and the cell value will change to 8, ie the full degree value of the "Westing" cell. Select the cell again and fill down to insert the data for the entire column.

    11. Place in cursor in Cell G2, type "=MID(C2,2,LEN(C2)-2)". Press return and the cell value will change to 56.847, ie the minute value of the "Westing" cell. Select the cell again and fill down to insert the data for the entire column.

    12. Now place the cursor in H2, type "=D2+E2/60". Press return and the value will change to 52.72077, ie the complete decimal degree latitude value. Select the cell again and fill down to insert the data for the entire column.

    13. Next place the cursor in I2, type "=-(F2+G2/60)". Press return and the value will change to -8.94745, ie the complete decimal degree longitude value. Select the cell again and fill down to insert the data for the entire column.

    14. Save the Excel file. In ArcGIS add Sheet1 of the Excel file.

    15. Right click and select Display XY Data. For X Field use Long, for Y Field Lat.

    16. For Coordinate System press Edit, then Select, choose Geographic Coordinate Systems-World-WGS 1984.prj

    17. Press OK for the ID field warning

    18. The data is added to the map. You can export it and project it to whatever system you want.


  • Registered Users Posts: 3,803 El Siglo


    lil*lady wrote: »
    Ok, decided to cut my losses and start from scratch, and it's working so far. Hurray. Thanks again!
    El siglo, I'd a quick look online and you can find converters to UTM...would that be any use to you? And then again I don't know, but there might be a way to import them into ArcMap with changing the coordinates the way YAT was saying before - I could be well off now, but just an idea...

    No, it can't be universal transverse mercator, it has to be the Irish Grid System. It's alright, I'll work it out somehow it's only a matter of converting the data!:pac:


  • Closed Accounts Posts: 85 ✭✭✭ YoureATowel


    Still having issues getting the DIVA roads layers to line up with my other layers.

    Just noticed this morning that the extent (General > Source) of the DIVA roads layer, having been projected to IRENET 95 ITM, is vastly different to the existing IRENET 95 ITM layers in my existing project.

    Existing layers:
    TOP: 459743.199900 m
    LEFT: 30161.660100 m
    RIGHT: 334528.400100m
    BOTTOM: 19703.940000 m

    DIVA Roads Layer (From WGS_84 to IRENET 95 ITM)
    TOP: 949553.281667 m
    LEFT: 431169.024752 m
    RIGHT: 728108.469048 m
    BOTTOM: 525182.475228 m


    Is there any way to manually change the extent to get the layers to sit on top of each other? I can't see what else I'm doing wrong, apologies if it's blindingly obvious!


    OK, the problem here is obvious. You downloaded the ED data from the CSO website. This data is in Irish National Grid but a *.prj file is not supplied.

    You have mistakenly assumed that the Electoral Divisions are in IRENET 95 ITM. Assuming that the image above is from an ongoing project do the following.


    1. Close the map.

    2. In ArcCatalog navigate to Irish ED ITM. Right click on it and select properties. For XY Coordinate System choose Irish National Grid.prj

    3. Start a new map in ArcView. Add the IRL Roads ITM data. Now add the Electoral Districts. the Geographic Coordinate Systems Warning will open telling you that you are adding data from a different coordinate system.

    4. Click close. The ED data is added and will overlay perfectly.

    5. Project the ED data from ING to IRENET 95 ITM to make a permanent copy in that system if you require.


  • Registered Users Posts: 3,803 El Siglo


    Usually if I was faced with this problem I would write a python script that would convert the data to a workable format. Here, as there are only a couple of points, you can do it manually.

    1. Open the data in Excel as you have shown

    2. In Cell D1 type "Long Degrees"

    3. In Cell E1 type "Long Minutes"

    4. in Cell F1 type "Lat Degrees"

    5. In Cell G1 type "Lat Minutes"

    6. In Cell H1 type "LONG"

    7. In Cell J1 type "LAT"

    8. Place in cursor in Cell D2, type "=LEFT(B2,2)". Press return and the cell value will change to 52, ie the full degree value of the "Northing" cell. Select the cell again and fill down to insert the data for the entire column.

    9. Place in cursor in Cell E2, type "=MID(B2,3,LEN(B2)-2)". Press return and the cell value will change to 43.246, ie the minute value of the "Northing" cell. Select the cell again and fill down to insert the data for the entire column.

    10 Place in cursor in Cell F2, type "=LEFT(C2,1)". Press return and the cell value will change to 8, ie the full degree value of the "Westing" cell. Select the cell again and fill down to insert the data for the entire column.

    11. Place in cursor in Cell G2, type "=MID(C2,2,LEN(C2)-2)". Press return and the cell value will change to 56.847, ie the minute value of the "Westing" cell. Select the cell again and fill down to insert the data for the entire column.

    12. Now place the cursor in H2, type "=D2+E2/60". Press return and the value will change to 52.72077, ie the complete decimal degree latitude value. Select the cell again and fill down to insert the data for the entire column.

    13. Next place the cursor in I2, type "=-(F2+G2/60)". Press return and the value will change to -8.94745, ie the complete decimal degree longitude value. Select the cell again and fill down to insert the data for the entire column.

    14. Save the Excel file. In ArcGIS add Sheet1 of the Excel file.

    15. Right click and select Display XY Data. For X Field use Long, for Y Field Lat.

    16. For Coordinate System press Edit, then Select, choose Geographic Coordinate Systems-World-WGS 1984.prj

    17. Press OK for the ID field warning

    18. The data is added to the map. You can export it and project it to whatever system you want.

    Thanks a million for that help.
    However, I'm still having trouble, I followed every single one of those steps and the data still isn't showing up. I tried to go to "zoom to layer" and the points come up but they're out of focus with the map, i.e. they're all over the page.

    It's probably me being retarded because your information was perfect and the points all came up.

    I really can't thank you enough for all the help!


  • Registered Users Posts: 6,032 ✭✭✭ Rowley Birkin QC


    OK, the problem here is obvious. You downloaded the ED data from the CSO website. This data is in Irish National Grid but a *.prj file is not supplied.

    You have mistakenly assumed that the Electoral Divisions are in IRENET 95 ITM. Assuming that the image above is from an ongoing project do the following.


    1. Close the map.

    2. In ArcCatalog navigate to Irish ED ITM. Right click on it and select properties. For XY Coordinate System choose Irish National Grid.prj

    3. Start a new map in ArcView. Add the IRL Roads ITM data. Now add the Electoral Districts. the Geographic Coordinate Systems Warning will open telling you that you are adding data from a different coordinate system.

    4. Click close. The ED data is added and will overlay perfectly.

    5. Project the ED data from ING to IRENET 95 ITM to make a permanent copy in that system if you require.

    You've done it again. Many thanks. :)

    However, that procedure seems completely counter-intuitive to what I would have expected to be doing given that one of my layers is in TM_65 ING and the other IRENET_95 ITM and yet they sit on top of each other perfectly. I'm probably showing my inexperience with GIS but how can this be?

    I've also dropped in the DIVA Rivers and Water Bodies layers, both unmodified from the original download projection (WGS_84), and everything is lining up perfectly! Good result but I don't understand it.


  • Closed Accounts Posts: 85 ✭✭✭ YoureATowel


    El Siglo wrote: »
    Thanks a million for that help.
    However, I'm still having trouble, I followed every single one of those steps and the data still isn't showing up. I tried to go to "zoom to layer" and the points come up but they're out of focus with the map, i.e. they're all over the page.

    It's probably me being retarded because your information was perfect and the points all came up.

    I really can't thank you enough for all the help!

    I used your first five points. Did you get the same results for LAT, LONG following the procedure? Note the negative values for LONG.

    Also in Display XY Data for X Field use LONG and for Y Field use LAT

    Image3.jpg


  • Registered Users Posts: 3,803 El Siglo


    I used your first five points. Did you get the same results for LAT, LONG following the procedure? Note the negative values for LONG.

    Also in Display XY Data for X Field use LONG and for Y Field use LAT

    Image3.jpg

    I just did it there now, had to switch the LONG and LAT in my excel file around, they were in the wrong places, just did it there now and it works like a charm! Thanks a million that fecking brilliant so it is!:pac:


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  • Closed Accounts Posts: 85 ✭✭✭ YoureATowel


    You've done it again. Many thanks. :)

    However, that procedure seems completely counter-intuitive to what I would have expected to be doing given that one of my layers is in TM_65 ING and the other IRENET_95 ITM and yet they sit on top of each other perfectly. I'm probably showing my inexperience with GIS but how can this be?

    I've also dropped in the DIVA Rivers and Water Bodies layers, both unmodified from the original download projection (WGS_84), and everything is lining up perfectly! Good result but I don't understand it.


    Consider the three main components of ArcGIS. They are ArcMap, which you would use for creating maps and editing the geometry of data. ArcCatalog which is used for exploring and managing GIS datasets. Finally there is ArcToolbox which is used for geoprocessing, ie creating derived datasets from your existing files.

    As I'm sure you've seen there are many ways in ArcGIS to achieve the same result. For example, in post #43 I've outlined how you can project data using either ArcMap or ArcToolbox.

    ArcToolbox can be used to permanently project a file from one XY coordinate system to another. To do this it has to know the transformation parameters. ArcToolbox can project between ING and WGS84, it can project between WGS84 and IRENET95_ITM, however it cannot project directly between ING and IRENET95_ITM as it doesn't have the necessary transformation parameters.

    ArcMap, on the other hand, can handle this projection. If you add IRENET95_ITM data to a map containing only ING datasets ArcMap carries out what is called on-the-fly projections. It looks at the newly added layer, it sees that it's in a different XY projected coordinate system. It will project the new data to it's geographic coordinate system, ie Lat, Long. ArcMap knows how to transform GCS_IRENET95 to GCS_TM65 which is used by ING. Next the GCS_TM65 data is projected to ING and can be displayed on the map. This does not create a permanent reprojected file.


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