# How to adjust online basemap to Arcmap

How can I adjust the online basemap imagery file to our existing ArcMap data. Below are steps I perform to add the basemap data.

1. I Added basemap from "Add Data From GIS Online" in the file menu and then selected Imagery and added to the Desktop.
2. I already have some layer files in our current project in arcmap the details of our

Qatar GCS (Datum) :

Qatar Projection: Transverse_Mercator

False_Easting: 200000.000000

False_Northing: 300000.000000

Central_Meridian: 51.216667

Scale_Factor: 0.999990

Latitude_Of_Origin: 24.450000

Linear Unit: Meter

GCS_International_1967

Datum: D_International_1967


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and the imagery from online data GCS(Datum) :

   WGS_1984_Web_Mercator_Auxiliary_Sphere

Projection: Mercator_Auxiliary_Sphere

False_Easting: 0.000000

False_Northing: 0.000000

Central_Meridian: 0.000000

Standard_Parallel_1: 0.000000

Auxiliary_Sphere_Type: 0.000000

Linear Unit: Meter

GCS_WGS_1984

Datum: D_WGS_1984


Now the problem is the added imagery data is looks like it's shifted around 100m difference with our arcmap hole data.

then I tried transformations to adjust with our arcmap data by selecting the same as our Datum: D_International_1967 in the dataframe properties but not changed anymore. and then i tried different transformations named as Qatar but same result not aligned the data.

am I trying to do the transformations at the right place.?? and any thing i missed here.???

1. **Right click in the arcmap\Datafareme properties\Coordinate system tab\Layers\selecting the desired layer to transform\transormations\convert from (selecting existing GCS)\into (Selecting desired GSC)
2. hit Ok.**
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I guess it would depend on the accuracy of the two datasets. Are you trying to overlay vectors to the basemap?? –  TsvGis May 29 '13 at 7:19
I'm just trying to add to my arcmap which currently working..because we have our own image files but this time not working properly so i wanted to add the basemap layer (imagery) after adding to the arcmap some how it's just aside from the original data in arcmap.. –  Ganeshnarim May 29 '13 at 7:33
What's the datum that your image is in? –  TsvGis May 29 '13 at 7:38
Datum: D_Qatar ( in our existing data) GCS_WGS_1984- Datum: D_WGS_1984 ( Online imagery file) –  Ganeshnarim May 29 '13 at 7:41
How much is the shift? On the order of 10's of meters, or many KM? How do you know that your vector data is positioned correctly? –  Devdatta Tengshe May 29 '13 at 11:15

You are trying to view data from two datums so will need to use a Transformation.

I'm not familiar with datums used in Qatar but on the Coordinate System tab of the Properties for your data frame you should be able to find a Transformations button which should offer you choice(es) based on which datums are in the data frame.

Try these steps using ArcGIS 9.3 (I am using ArcGIS 10.1 SP1 but the steps should be basically the same):

1. Start ArcMap with a Blank Map
2. Use Add Data | Add Basemap to add the Imagery basemap
3. Use the Find tool to locate and Zoom To the State of Qatar - then set the scale to 1:250000
4. Use the Coordinate System tab of the Properties for the Basemap layer and you should see that it is WGS_1984_Web_Mercator_Auxiliary_Sphere
5. To change the Coordinate System of the Data Frame for display (do NOT use the Layers part of the dialog) choose Predefined>Projected Coordinate Systems>National Grids>Asia>Qatar National Grid.
6. Hit the Transformations button and chose to Convert from GCS_WGS_1984 to GCS_Qatar_1974 using Qatar_1974_To_WGS_1984_3
7. Hit OK to accept the Transformation and OK again to display the map in the Qatar National Grid coordinate system

I don't have any data to add and observe the result but am confident that if it was in Qatar National Grid it would line up. However, depending on where in Qatar it was it might be that Qatar_1974_To_WGS_1984_1 or Qatar_1974_To_WGS_1984_2 were slightly better than my first choice above.

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Why would a datum transformation be required if the map service, as well as the vector data, both are in WGS84 datum? –  Devdatta Tengshe May 29 '13 at 11:14
I read D_Qatar as being potentially a variation on WGS84 but am no geodesist so happy to defer to you on this. –  PolyGeo May 29 '13 at 11:47
Ok Got it. I misread that as being WGS84 as well. –  Devdatta Tengshe May 29 '13 at 13:29
I tried transormations in dataframe properties but i came up with no luck. is there any other way to adjust the map with data.? –  Ganeshnarim May 29 '13 at 18:18
Which transformation method did you choose to try? Also, I would recommend you revise your question to provide detailed steps starting with Blank Map for how you try to align one dataset with the online basemap. –  PolyGeo May 29 '13 at 19:55