There are specific positions on all maps where he can deal the max damage of 125 from his Seismic Slam. A reddit user went fairly in depth with this guide:d
An example using Dorado's 2nd stage:
#Dorado
Intended landing point:
This high ground to the right of section B
#Eichenwalde
Seismic Slam use point:
The highest point of the castle in payload section A
Locations#Hanamura
The three highest positions of high ground on Point B to performthe lowest ground in front of Point B:
1: The arch
2: The easiest-access one
3: The "Widow high ground"
The highest point of the choke on Point A
EDIT: The top of this building next to Point A
#Hollywood
The catwalk above payload section A
The platform under the water tower Torbjorn players almost certainly use at the control point
#Horizon Lunar Colony
This excruciatingly slow moving platform above point B
#Ilios: Lighthouse
This very high ground on the lighthouse
#Ilios: Well
This very high ground on the building next to the well
#Ilios: Ruins
#King's Row
The head of the Mondatta statue
The highest entrance of the attacker spawn
#Lijiang Night Market
The highest point of the buildings just outside the spawn rooms (almost completely useless)
#Lijiang Garden
Nothing! There is no ground on Lijiang Garden that is both high enough for a 125 damage slam and low enough for Doomfist to reach.
#Lijiang Control Center
#Nepal Village
Nothing! There is no ground on Nepal Village that is both high enough for a 125 damage slam and low enough for Doomfist to reach.
#Nepal Shrine
Nothing! There is no ground on Nepal Shrine that is both high enough for a 125 damage slam and low enough for Doomfist to reach.
There is an elephant statue that is high enough to land on the low ground next to the control point with a healthpack on it, but you cannot control the Slam arc enough to actually hit the ground. You just leap off the cliff.
#Nepal Sanctum
The top of these buildings outside the spawn rooms (almost completely useless)
#Numbani
Nothing! There is no ground on Numbani that is both high enough for a 125 damage slam and low enough for Doomfist to reach.
Ironic, isn't it? The map where Doomfist wrecked OR-15s in the airport is one of the few that he cannot perform a full-power Seismic Slam in unassisted.
#Oasis City Centre
Uhh... inside one of the spawn rooms? (this one is so useless I didn't even put it in an imgur album)
#Oasis Gardens
#Oasis University
Nothing! There is no ground on Oasis University that is both high enough for a 125 damage slam and low enough for Doomfist to reach.
#Route 66
The railing on top of "The High Side" building in the middle of section B
This rock pillar at the start of section A
#Temple of Anubis
This high ground in front of Point B (very popular Widowmaker spot)
EDIT: The similar high ground in front of point A (someone found a way up there)
- Dorado
- Eichenwalde
- Hanamura
- Hollywood
- Horizon Lunar Colony
- Ilios
- King's Row
- Li Jiang
- Nepal
- Numbani
- Oasis
- Route 66
- Temple of Anubis
- Volskaya Industries
- Watchpoint: Gibraltr
#Volskaya Industries
The highest point of this building in front of the attackers' spawn (works in both directions)
#Watchpoint: Gibraltar
The two highest points able to reach the lowest ground on section A
The highest point overlooking the end of section A (I actually forgot to get screenshots of this one, I'm afraid. It's the same high ground as "1" listed eariler, just closer to the end)
This incredibly high ground overlooking the start of section C