So If I'm understanding this correctly, you want to clip a raster (top layer) by a polygon (London Boundaries). And the software you are using is ArcGIS Desktop 10.6.
If that is the case, one workflow would be this:
1. As suggested by Xander Bakker, run the geoprocessing tool Dissolve (Data Management) on the London Boundaries to simplify it to one polygon boundary.
2. Run the Clip (Data Management) geoprocessing tool, specifying for "Output Extent (optional)" the feature class created from the Dissolve and checking the box to employ "Use Input Features for Clipping Geometry (optional).
Dissolve—Help | ArcGIS for Desktop
Clip—Help | ArcGIS for Desktop
Chris Donohue, GISP
If you use Clip—Help | ArcGIS Desktop on two polygon layers, it will clip the input polygons using the clip polygon (exactly). Both your layers are polygons? To avoid any redundant intersection you could dissolve the clip features (if they are multiple polygons) into a single polygon using Dissolve—Help | ArcGIS Desktop
Thanks for your reply, the lower layer (London boundaries) is a polygon, top layer is a raster
If you are trying to clip the raster by the outline of the polygons, you could also set it as Mask and do a simple Raster Calculation that returns the raster: Mask (Environment setting)—Help | ArcGIS Desktop or use Extract by Mask—Help | ArcGIS Desktop
That worked perfectly, thank you for the clear explanation!
Its nice to see that and like a appreciated your endeavor.Keep it up to more
Retrieving data ...