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I'm currently working with OS data and have just tried to import a table of google maps coordinates/point data into ARC. The data frame (& layer) coordinate system is as follows:

British_National_Grid WKID: 27700 Authority: EPSG

Projection: Transverse_Mercator False_Easting: 400000.0 False_Northing: -100000.0 Central_Meridian: -2.0 Scale_Factor: 0.9996012717 Latitude_Of_Origin: 49.0 Linear Unit: Meter (1.0)

Geographic Coordinate System: GCS_OSGB_1936 Angular Unit: Degree (0.0174532925199433) Prime Meridian: Greenwich (0.0) Datum: D_OSGB_1936 Spheroid: Airy_1830 Semimajor Axis: 6377563.396 Semiminor Axis: 6356256.909237285 Inverse Flattening: 299.3249646

I've imported the coordinates from google maps as a table, exported it as a shapefile defining the coordinate system to Spherical Mercator (ESPG 3857). I've then imported the data, transformed it to the above projection, in the hope that the two would align. The area of interest is London, and the points appear far further south than they should be - several lengths of the UK further south (but approximately at the right longitude).

Can anyone suggest what I might be doing wrong? I'm at a loss after having followed various online tutorials and how-tos. Sorry if this seems obvious - I'm a beginner.

Thanks -

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1 Answer 1

up vote 4 down vote accepted

For the points you gathered from google maps, you should use WGS1984:

GCS_WGS_1984 Authority: Custom

Angular Unit: Degree (0.0174532925199433) Prime Meridian: Greenwich (0.0) Datum: D_WGS_1984 Spheroid: WGS_1984 Semimajor Axis: 6378137.0 Semiminor Axis: 6356752.314245179 Inverse Flattening: 298.257223563

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+1. Google maps coordinates are in WGS1984. You will first need to define the coordinate system after you bring the points in. Once you define the coordinate system as WGS1984, you can then project the points into whatever coordinate system you desire, such as the coordinate system of your data frame, British_National_Grid WKID. I wish Google's coordinate system was more explicitly stated on their website as at the time of this posting there is no mention of it on Google's main map support website. –  Conor Aug 21 '13 at 18:08
    
I think Google prohibits both personal and enterprise users to use their data in raw format. They expect you to utilize their services and APIs. That's probably why they see no reason to share such info. –  Anıl Çelik Aug 21 '13 at 18:22
    
I can't find a way of creating a custom WGS in ARC when I add the xy data. The details seem to match WGS_1984_Web_Mercator_Auxiliary_Sphere WKID: 3857 Authority: EPSG - is this the right one to use? I don't know what to do next to fix this –  Joules Aug 22 '13 at 9:23
    
Thanks Conor & Anil - I figured it out with your help. I was projecting on import. –  Joules Aug 22 '13 at 16:47

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