In this article, we will talk about the fundamental principles of modeling terrain landscape.
Facing a terrain project,where should we begin ? Although it is a puzzling question, there is one thing we can confirm :all works of terrain modeling are base on a net of roads.If a part of road is modified,all things connected with that road will have to be adjusted.For example,if you first make the curbs of a road and then change the elevation of the road,previous work will be wasted.So,the most logical principles should be :First build a road as accuratly as possible ,then think about how to add new faces to connect the between road and the terrain.
In general,three issues are focused by 3D modeling artists:good topology,the presentation of slopes and rolling roads , the connecting if the road with the terrain.
First of all,we talk about the question paid most attention to by 3D modeling artists :how to connect the road and terrain

1 The connection of roads and terrains

There are two main ways to connect roads and terrains:
1.For terrain that already exists,such as a terrain built from contour lines or DEM data,you can first delete the faces covered by the roads,then stitch their boundary together .
This task can be usually done by creating a big polygon with its borders,then using StitchVerts to cut the new polygon to get reasonable topology.StitchVerts is the most efficient way to connect vertices,as it can quickly stitch different polygons together.If you are using the Lite version ,advConnectVts is an alternative.

Use StitchVerts connect roads and terrains

2.For those areas enclosed or semi-enclosed  by  roads,maybe the original terrain is missing or un-useful,new terrain need to be re-created. Thus you can cap these areas to create a new polygon,then use Slice to cut and get grid-like topology,then relax them or paint desired appearance with 3dsmax’s brush tools .

Create terrain with Slice

the way is also suit for first situation.If you don’t like the topology created with contour lines,you can use MoveVerts to conform vertices of the grid-like faces to original terrain.So,you need not to stitch them.

Use MoveVerts re-construct terrain

2 Topologizing

To express sloped landscape and ups ans downs of road, topologizing or re-topologizing   is necessary.There are some requirements for topologizing:A road should be made up of continuous quad polygons as much as  possible,as shown  below in left picture;Some ground pavement need some cutting operations to make the polygon topology more reasonable;Narrow and long triangles should be avoided as much as possible. The more reasonable topology, the better the effect at render time, as shown below in the right picture.

Good topology1

Good topology2

For achieve above goals,some cutting tools will be often used,such as CutPerToEdge(cut perpendicularly to edge),CutByAgl(cut along angular bisector from vertices on border),Cut2Verts(cut between 2 vertices),Connectverts and StichVerts(connect two team of vertices) ,and so on

Cut perpendicularly to edge

Cut along angular bisector

Connect two vertex team

Road can be created by SweepEdge with mid-lines.

Mid-lines of road

Road created by SweepEdge

Some weld tools are also necesseray

3 Slope pavement and ups and downs of road

Slope pavement
Such a tool is indispensable:when vertices of surface fall to slope,only z coordinates are modified but xy coordinates keep unchanged,that is ,make vertices align to slope plane along Z axis ,or the structure in top view will be damaged.MoveVerts can do this.

Slope landscape

Ups and downs of Road
On expressing ups and downs of road,notice that the road should always keep its section horizontal,can’t stick on terrain like cloth .So the tool  should be, with selected edges on one side of road and several vertices at special elevation,which can output the smooth transition of curve and meanwhile map this side of the evelation data to the other side,thus we can get the road to transit smoothly between elevations.
you can use smoothroad(linear),SmoothRoad(curve),SmoothRoad(npts),SmoothRoad(blur) to complete this work.

Use SmoothRoad(blur)to smooth road

The article describe only several  main issuses of landscape modeling from the outer frame,it should be as a main direction.Hope that every readers can get desired help and have a good beginning.