Why does a map layer appear shifted?
A GIS layer that appears shifted relative to satellite imagery does not have one universal software fault. A wrongly assigned source coordinate reference system, datum transformation, image georeferencing, resolution, data date or differing feature definition can each explain a mismatch. Read the actual coordinate metadata first and measure displacement at independent stable points.
Separating possible causes
1. What happens when the CRS label is wrong? If stored latitude-longitude numbers are declared to be UTM meters, software places them wrongly without understanding their true meaning. Assigning a source CRS is different from transforming numerical coordinates into another system. On-the-fly transformation can make layers look aligned on a screen while leaving the files unchanged. Inspect metadata, coordinate ranges, units and the producing institution's description first. A layer that looks better after choosing WGS84 has not thereby been proven correct. Saving a guessed definition can make the original provenance hard to reconstruct. 2. What shift can datum differences cause? The same numbers in different horizontal reference frames can correspond to different physical places. USGS explains positional differences between older and newer North American datums when historical maps are compared with modern GPS. That example does not justify using the same parameters in other countries. Identify source and target datum, transformation operation, required grid and area of validity. Differences in vertical reference are a separate question from horizontal displacement; a height profile mismatch needs its own investigation. 3. Why might image georeferencing be wrong? An old paper sheet, drone photograph or aerial image may not have been fitted to stable ground locations. The QGIS Georeferencer uses control points matched to known coordinates. Incorrect matches, points clustered in one corner or a coastline that has moved can create local errors. Missing terrain correction in satellite imagery can worsen misalignment on steep slopes. Remember that a third-party basemap used as a reference can itself contain positional error; agreement with it is not a universal ground truth test.
Measuring, correcting and reporting
4. What does the shape of displacement reveal? Similar direction and distance at many stable points suggest a systematic offset. Increasing rotation or stretching toward the edge may indicate a projection issue, warped scan or poorly distributed control points. A discrepancy only at one river bend may reflect real channel change or different acquisition dates. Tabulate coordinate differences at several independent features across the scene. Measure in ground units rather than counting display pixels at one zoom level. Check whether discrepancies repeat across products from the same provider. 5. Which repair matches which problem? Correcting an incorrectly assigned CRS label does not change stored coordinate numbers. Reprojection from the actual source system to a target produces new coordinates. Georeferencing a scan with no reliable location is a separate control-point fitting operation. Dragging an entire layer by eye hides the underlying cause and can increase error elsewhere. Keep the original file and a separate corrected output; document the operation and errors at independent checkpoints. A fit that looks good only at the matched points may not be reliable beyond them. 6. When might the difference be real change? A new road, filled shore, shifted river or rebuilt structure may actually occupy a different place. Verify data dates and the definition of what each map depicts. Do not expect a road centerline to match a sidewalk edge exactly. Cadastral, construction and infrastructure work needs authoritative survey data and on-site checks, not visual alignment alone. State source and output CRSs, dates, sampled offsets and remaining uncertainty whenever a repaired layer is shared.