I rather like what you did with the map there. That's pretty cool looking.
The different terrain types all have different movement characteristics, which affects units differently based on their track types (wheeled, tracked, legged). It also affects blight spread speed. Blight spreads slower on lava rock. Day/night also affects blight spread speed, where is spreads slower at night, though that is independent of the terrain type. Each cell type has an array of speed/spread values for each movement type. The range of values is quite large, and varied between similar cell types, though the observed effect in game may be small and hard to notice between similar cell types.
There are some unknowns in the data. It seems to consist of 32 terrain types, each with 8 track type movement values. A hex dump of the movement values exists in the SVN in
OllyDbg/InternalData/Data CellTypes.txt:
Terrain type data
-----------------
Note: There are 32 terrain types.
Note: The following Track Types are found in vehicles.txt
T - tracked
W - wheeled
M - ? (GeoCon and RoboMiner) - type 3
L - legged
- blight - type 7?
004DEBA8 004DEB98 ASCII "Fast Passible 1"
004DEBAC 00000E00
004DEBB0 00001000
004DEBB4 00001000
004DEBB8 00001000
004DEBBC 00000000
004DEBC0 00000000
004DEBC4 00000020 ; Blight spread speed
004DEBC8 00001666
004DEBCC 004DF190 ASCII "Impassible 2"
004DEBD0 00000000
004DEBD4 00000000
004DEBD8 00000000
004DEBDC 00000000
004DEBE0 00000000
004DEBE4 00000000
004DEBE8 00000010
004DEBEC 00003D86
004DEBF0 004DF180 ASCII "Slow Passible 1"
004DEBF4 00001600
004DEBF8 00001A00
004DEBFC 00001A00
004DEC00 00001A00
004DEC04 00000000
004DEC08 00000000
004DEC0C 00000010
004DEC10 00000000
004DEC14 004DF170 ASCII "Slow Passible 2"
004DEC18 00001A00
004DEC1C 00001800
004DEC20 00001800
004DEC24 00001600
004DEC28 00000000
004DEC2C 00000000
004DEC30 00000018
004DEC34 00004A46
004DEC38 004DF15C ASCII "Medium Passible 1"
004DEC3C 00001400
004DEC40 00001400
004DEC44 00001400
004DEC48 00001200
004DEC4C 00000000
004DEC50 00000000
004DEC54 00000018
004DEC58 00007BC5
004DEC5C 004DF148 ASCII "Medium Passible 2"
004DEC60 00001200
004DEC64 00001600
004DEC68 00001600
004DEC6C 00001400
004DEC70 00000000
004DEC74 00000000
004DEC78 00000018
004DEC7C 000056B5
004DEC80 004DF138 ASCII "Impassible 1"
004DEC84 00000000
004DEC88 00000000
004DEC8C 00000000
004DEC90 00000000
004DEC94 00000000
004DEC98 00000001 ; lava speed control?
004DEC9C 00000010
004DECA0 00002D6B
004DECA4 004DF128 ASCII "Fast Passible 2"
004DECA8 00001000
004DECAC 00001000
004DECB0 00001000
004DECB4 00001000
004DECB8 00000000
004DECBC 00000000
004DECC0 00000020
004DECC4 00003B6A
004DECC8 004DF118 ASCII "North Cliffs"
004DECCC 00000000
004DECD0 00000000
004DECD4 00000000
004DECD8 00000000
004DECDC 00000000
004DECE0 00000001
004DECE4 00000010
004DECE8 00007640
004DECEC 004DF104 ASCII "Cliffs - High side"
004DECF0 00000000
004DECF4 00000000
004DECF8 00000000
004DECFC 00000000
004DED00 00000000
004DED04 00000001
004DED08 00000010
004DED0C 00007640
004DED10 004DF0F0 ASCII "Cliffs - Low Side"
004DED14 00000000
004DED18 00000000
004DED1C 00000000
004DED20 00000000
004DED24 00000000
004DED28 00000000
004DED2C 00000010
004DED30 00007640
004DED34 004DF0DC ASCII "Vents and Fumaroles"
004DED38 00000000
004DED3C 00000000
004DED40 00001A00
004DED44 00000000
004DED48 00000000
004DED4C 00000001
004DED50 00000010
004DED54 00001B19
004DED58 004DF0D4 ASCII "zPad 12"
004DED5C 00000200
004DED60 00000200
004DED64 00000200
004DED68 00000200
004DED6C 00000200
004DED70 00000000
004DED74 00000020
004DED78 00006000
004DED7C 004DF0CC ASCII "zPad 13"
004DED80 00000155
004DED84 00000200
004DED88 00000200
004DED8C 00000200
004DED90 00000200
004DED94 00000000
004DED98 00000010
004DED9C 00004000
004DEDA0 004DF0C4 ASCII "zPad 14"
004DEDA4 00000400
004DEDA8 00000000
004DEDAC 00000000
004DEDB0 00000400
004DEDB4 00000000
004DEDB8 00000001
004DEDBC 00000010
004DEDC0 00000200
004DEDC4 004DF0BC ASCII "zPad 15"
004DEDC8 00000000
004DEDCC 00000000
004DEDD0 00000000
004DEDD4 00000000
004DEDD8 00000000
004DEDDC 00000001
004DEDE0 00000000
004DEDE4 00004210
004DEDE8 004DF0B4 ASCII "zPad 16"
004DEDEC 00000200
004DEDF0 00000200
004DEDF4 00000200
004DEDF8 00000200
004DEDFC 00000200
004DEE00 00000000
004DEE04 00000020
004DEE08 00006000
004DEE0C 004DF0AC ASCII "zPad 17"
004DEE10 00000200
004DEE14 00000200
004DEE18 00000200
004DEE1C 00000200
004DEE20 00000200
004DEE24 00000000
004DEE28 00000020
004DEE2C 00006000
004DEE30 004DF0A4 ASCII "zPad 18"
004DEE34 00000200
004DEE38 00000200
004DEE3C 00000200
004DEE40 00000200
004DEE44 00000200
004DEE48 00000000
004DEE4C 00000020
004DEE50 00006000
004DEE54 004DF09C ASCII "zPad 19"
004DEE58 00000200
004DEE5C 00000200
004DEE60 00000200
004DEE64 00000200
004DEE68 00000200
004DEE6C 00000000
004DEE70 00000020
004DEE74 00006000
004DEE78 004DF094 ASCII "zPad 20"
004DEE7C 00000200
004DEE80 00000200
004DEE84 00000200
004DEE88 00000200
004DEE8C 00000200
004DEE90 00000000
004DEE94 00000020
004DEE98 00006000
004DEE9C 004DF088 ASCII "Dozed Area"
004DEEA0 00000C00
004DEEA4 00000C00
004DEEA8 00000C00
004DEEAC 00000C00
004DEEB0 00000C00
004DEEB4 00000000
004DEEB8 00000020
004DEEBC 00007FE0
004DEEC0 004DF080 ASCII "Rubble"
004DEEC4 00001000
004DEEC8 00001000
004DEECC 00001000
004DEED0 00001000
004DEED4 00001000
004DEED8 00000001
004DEEDC 00000020
004DEEE0 00004200
004DEEE4 004DF074 ASCII "Normal Wall"
004DEEE8 00000000
004DEEEC 00000000
004DEEF0 00000000
004DEEF4 00000000
004DEEF8 00000000
004DEEFC 00000001
004DEF00 00000020
004DEF04 00006000
004DEF08 004DF064 ASCII "Microbe Wall"
004DEF0C 00000000
004DEF10 00000000
004DEF14 00000000
004DEF18 00000000
004DEF1C 00000000
004DEF20 00000001
004DEF24 00000010
004DEF28 00006000
004DEF2C 004DF058 ASCII "Lava Wall"
004DEF30 00000000
004DEF34 00000000
004DEF38 00000000
004DEF3C 00000000
004DEF40 00000000
004DEF44 00000001
004DEF48 00000020
004DEF4C 00006000
004DEF50 004DF050 ASCII "Tube0"
004DEF54 00001000
004DEF58 00001000
004DEF5C 00001000
004DEF60 00001000
004DEF64 00001000
004DEF68 00000000
004DEF6C 00000020
004DEF70 00000210
004DEF74 004DF048 ASCII "Tube1"
004DEF78 00001000
004DEF7C 00001000
004DEF80 00001000
004DEF84 00001000
004DEF88 00001000
004DEF8C 00000000
004DEF90 00000020
004DEF94 00000210
004DEF98 004DF040 ASCII "Tube2"
004DEF9C 00001000
004DEFA0 00001000
004DEFA4 00001000
004DEFA8 00001000
004DEFAC 00001000
004DEFB0 00000000
004DEFB4 00000020
004DEFB8 00000210
004DEFBC 004DF038 ASCII "Tube3"
004DEFC0 00001000
004DEFC4 00001000
004DEFC8 00001000
004DEFCC 00001000
004DEFD0 00001000
004DEFD4 00000000
004DEFD8 00000020
004DEFDC 00000210
004DEFE0 004DF030 ASCII "Tube4"
004DEFE4 00001000
004DEFE8 00001000
004DEFEC 00001000
004DEFF0 00001000
004DEFF4 00001000
004DEFF8 00000000
004DEFFC 00000020
004DF000 00000210
004DF004 004DF028 ASCII "Tube5"
004DF008 00001000
004DF00C 00001000
004DF010 00001000
004DF014 00001000
004DF018 00001000
004DF01C 00000000
004DF020 00000020
004DF024 00000210
Disaster occurrence is independent of cell type. That is set separately from the level DLL using Triggers. Though the level designers do tend to associate certain disasters with certain areas of the maps / types of terrain.
I believe cliffs are supposed to have a noticeable effect on blight spread speed.
The bottom row of the map is always marked as impassible. I suspect that was to cover over potential bounds checking bugs with unit movement. Additionally, the map's clip Rect will also reflect the bottom row being impassible.
As for the tops of plateaus being marked as impassible, that may have been a custom modification to the levels done in one of the OPU releases. I suspect if you go back to a stock Sierra release, that won't be the case. I think it was modified to prevent units from spawning on top of plateaus by accident. That could happen if a vehicle factory is completely surrounded by units, and still pumping out units. The units spawn in a spiral pattern around the vehicle factory. Eventually they may spawn far enough away to appear on a plateau, where they would be stuck. If you drove the unit into the middle of a plateau, out of weapons range, it might deadlock a match, as there could be no way for an opponent to kill the unit.