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# Overlaying

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02-15-2017 04:18 AM
New Contributor II

Hi please help me it is very urgent...i have a vector data of 1:25000 which was digitized and the raster is of 1:50000...so now i wan the vector data to aligned with the toposheet of 1:50000 as their is a shift when i overlay the vector data on 1:50000 toposheet..how can it be done so that the vector data is aligned on 1:50000 toposheet..please help me..thank youw

16 Replies
MVP Alum

How far is the shift?

They will always be differences if these 2 datasets are from different sources and scales.

Coordinate system? Datum shift?

New Contributor II

Yes they we're digitized of different scales the vector data is of difeerent scale its of 1:25000 wheras i have a toposheet of 1:50000 so i want to know if i can do anything with it or not...since the drainage and roads are shifting even though i overlay on google earth...so is there a way to correct the data..

MVP Emeritus

right-click on each layer and examine its properties, the coordinate system specifically and the datum in particular.  If the datums are different, (ie NAD27 vs NAD83) then you need to use the Project tool to project one to the other.  If one doesn't have a defined coordinate system (ie it is undefined) you had better find out what it is, then use the Define Projection tool prior to using the Project tool if needed.

New Contributor II

both the data are of correct projection...but the shift is still there even for drainage and the roads....even when i overlay on google earth the shift is still there...

MVP Emeritus

Just because a coordinate system is defined, doesn't mean it is defined correctly a consistent shift is generally an indicator of an inappropriate use of the Define Projection tool at some stage of the history of the file particularly if the shift is consistent within the map and ... for some area... in the 100s of meters.

Can you provide some values for the shift?  Whether the shift is the same in all cardinal directions? Also note, that maps digitized from sources at different scales won't align exactly because of errors during the digitizing process.

New Contributor II

its around 200m...few are 100 m...300 m shift.....the vector data we're digitized at a scale of 1:25000 and i have a toposheet of 1:50000 so i wan to overlay it in 1:50000 so is there any method wer i can align them at 1:50000

MVP Alum

If it was all around 200-300m I would definitely point to a datum difference between the 2 datasets.

Have you tried overlaying the data on top of some of the online basemaps like imagery or something?

What do you see in terms of alignment?

New Contributor II

ive tried on google earth the shift is still there ..n even on geoeye of 5 m resolutions there's still a shift...what to do???

MVP Emeritus

show an image of what you are talking about, it could be you are just trying to reference bad digitizing if there is no pattern to the problem