I want to edit a terrain region in FSX, its a tabletop airport and I want to have slopes. Default airport is totally flat. I tried elevation and flattening but it makes it to look like a step, not a slanted slope.
Please explain more clearly what it is that you wish to achieve at the airport.
Bear in mind that sucessful function of default or custom AI Traffic and Ground vehicles must have a flattened surface for any Taxiways and Aprons that are all at the same elevation as RWYs and the Airport Reference Point (aka "ARP").
The opening post of this threads read as though you are wanting to blend the airport area into the surrounding terrain.
If you state the ICAO code of the airport that this is for, we will know what the real world terrain is surrounding that airport,
and it would then be easier to advise whether it may be preferable to use a:
* custom terrain mesh compiled via SDK Resample
* CVX vector 'sloped flatten' compiled via SDK SHP2VEC
You should be able to achieve a general improvement in local terrain shape by using at least the freely-downloadable "FreeMesh-X" 30 Meters between elevation data points terrain mesh BGL(s), and then using a custom 3D model TIN surface of the local airport terrain that blends the central airport flatten into the surrounding terrain mesh.
That custom 3D TIN terrain surface model can be imported into Arno's ModelConverterX (aka "MCX"), then exported as a CVX vector terrain "sloped flatten" BGL.
If you would like to explore these options, feel free to inquire further and I can provide you with additional details.
Manually constructing a custom TIN or TRN surface without gaps or mis-aligned vertices / edges that also blends properly from the edge of the central airport flatten outwards into the terrain surrounding an airport of that size ...will be challenging to do "properly" in ex: ADE; but it is certainly possible if you are willing to do all the work that method will require.
If you have experience in 3D modeling, you could perform the task much easier, IMHO, by the process I cited above.
Alternatively, in SBuilderX, you could manually construct a more accurate CVX vector sloped flatten over a continuously scroll-able high resolution aerial imagery background with the assistance of a superimposed FS LOD-21 / QMID-23 quad mesh terrain grid as discussed in this thread: