What is a DEM (Digital Elevation Model

[Mimi]

That was an Excellent surveying info Mr Eslam

About this I've read That American Surveyors usually use The Term DEM which includes only elevation
data that are generally not considered as terrain surface. In most cases DEM is grid data with elevation attributes, which is suitable to use for analyses in raster GIS

But Canadian Surveyors usually use The Term DTM which includes more general information than DEM

DTM is a modeled surface structure which contains also other data of terrain as following: ridgelines, peak points etc

So if u don't Mind Mr Eslam ..Could you Explain more the difference Between the both terms later in the Arabic Topic? and Thanks any way