Greflin, were you on there when we were playing de_view? I can't remember .

I went around de_view and de_menace_final marking up the areas the sniper can see and (for view) areas that are safe from the sniper.

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de_view:
http://www.swrebellion.com/igor/de_view_sniper.jpg

The red highlighted areas are where the sniper can pretty much see, I did a lot of this by running around all over the map with a scout and seeing from where the sniper can shoot you and where the sniper can't.

Blue areas denote areas where you can run around safely with the sniper not seeing you. I tried to make the areas closest to A the most accurate, since that's what CTs are supposed to be defending.

The red X is where the bomber can plant so the sniper doesn't see him or bomb (incase CTs take over the sniper nest).

The green circles are the positions with the most visibility of A, also with the most cover. For the circles in the buildings on the left, you'll have to go on the window ledge to get better visibility. If you are on the circles on the right half, you'll probably need smokes to run past sniper visibility areas to B if B site is jeopardized.

Conclusions:
It is still possible to defend bomb site A very well even with a sniper in the tower, but it will be somewhat harder if Ts manage to plant the bomb down in the middle. Incase CTs need to move from B to A, they can safely get in range by going underground B to stairs at A (but riskier using ladder at B).

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de_menace_final:
http://www.swrebellion.com/igor/de_menace_sniper.jpg

Red highlighted areas are the same as before. Dark red area is what I count as the sniper area this time, since there's no clear tower. There are no blue areas, the sniper can't see anywhere its not red instead.

The green X is where the bomber can plant so the sniper can (barely) see someone defusing it. You have to do it all the way on the top-left edge of the bomb site.

If the CT defuses the bomb in that spot while standing he will get shot by the sniper very quickly. If crouching, he will be much harder to hit but still doable because you can see the top of his head.

If the sniper moves up past the white car 3 seconds north of his spot, he will gain much better visibility of the defuser and should even be able to get a HS on him while crouching. On the flip side, there will be much less cover there against CTs with Bullpups (and M4 is less significant that far away).

CTs should be at both green dots to be able to watch the entire bomb site A. While they won't be shot by the sniper, they will be able to do almost nothing (except throwing grenades) against Ts who rush up the river/side. This is in contrast with de_view, where you can cover a much larger radius around the bomb site without being afraid of the sniper.

There are 3 other areas near A (2 in the water, 1 closer to A by the brick roofs) that you can be safe from the sniper at, but they are marginalized because the west water spot is too far away from A, the south water spot too close to Ts to get there before they do, and the non-water spot has no cover and a CT will be mowed down by Ts rushing up stairs if he goes there.

Also note that if the sniper keeps moving around, he will be able to see CTs coming down the middle route, potentially sniping them before they are able to arrive through A going to middle (or at least notifying his teammates they are coming). The only 100% safe route from B to A is to go through CT spawn (wasting valuable time) as CTs.

Other important observations:
If the CT sniper at A is crouching, he will not be able to see the T sniper at double doors. At that very long range, it is very very hard to get a headshot on the enemy while standing, since the bullet seems to go to the side no matter what. But the T sniper can crouch down there, and have 100% accuracy and headshot the CT sniper with ease. Given two equal skill snipers, the T sniper will take out the CT sniper almost all of the time because of this.

Conclusions:
The Ts should always try to plant the bomb on the green X. As long as there is a good sniper near double doors, and nobody rushes the sniper from the middle, the Ts will have someone to fall back on incase the CTs break through the T defence after the bomb has been planted. However, if the Ts are assaulting A, then the CTs will be hardpressed to do much until the Ts are practically at A.

This could be a good strategy:
If CTs hold double doors where the T sniper would usually be, the Ts will be cut off from the sniper. They also won't be able to assault A through double doors very successfully, since they'll probably get shot as soon as they pass through them. They will only be able to get to A through B, where there will be just as many CTs. If the Ts do decide to go to B, flanking the Ts by going south and then east could be invaluable. Otherwise, it is only necessary to defend DD and B.
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Actually maybe I could even turn these pictures into some kind of guides for TG newcomers or for people who don't know the maps well.