Basics: Perches

A perch is a bookmark located near to an area of interest.  A perch is designed to enable observation and/or tactical mobility in that area, while denying equal observation and mobility to potential enemies.  The label "perch" suggests a high place a bird of prey might alight, allowing it to observe the ground around it and possibly swoop down to attack.

Type of Perches

Perches may be onor off a "grid" of interest, depending on their use.  What is a grid?  A grid is a volume of simulated space.  Ships and other objects on the same grid show up on each other's overview (if uncloaked), and can be interacted with (assuming the range allows).  Ships and objects on different grids, no matter how close they are to each other, do not appear on overview and cannot be interacted with.  How close can they be?  Arbitrarily close.  Adjacent grids have "grid walls": an invisible boundary between them.  Two ships on either side of a grid wall can be 1km away and still not see each other.  

A perch used only for observation is generally best off-grid.  ("Observation" in the case of off-grid means observation via the directional scanner, aka "dscan".)  An off-grid perch makes it hard for an enemy to even know you are near.  The only way he can find out is via dscan, which is a much harder and less informative method than looking at overview.  Even once he notices you are there, it takes additional work to determine your range and direction.  

A perch used for PVP must be on-grid.

Creating Perches

Creating a perch is simple in theory.  Move your ship to the location you want.  Then make a bookmark.

For an on-grid perch, you want to get at least 150km from every point on grid you might want to warp to.  The reason for the 150km is that 150km is the minimum distance that EVE allows initiating a warp.  Note that warping to N (10, 20, 30, 50, 70, 100) is allowed no matter what the warp distance is.  So you can do a warp of 50km, but only if there is a warpable object at least 150km in that direction.

In practice, flying 150km takes time.  If you have a microwarpdrive and a fast ship it helps a lot.  You can also speed things up by warping off grid, then warping back at 100km.  You can then either slowboat backwards 50km, or make a temporary bookmark, warp off again, then warp to the temporary bookmark at 100km again.  This gets you 200km off from the initial location chosen, which is a good on-grid bookmark.  

For an off-grid perch, you want to get off the grid (duh).  Often, 300km will be off-grid.  However, that is not always true.  Grids are not spheres or any particular shape; they are not even necessarily convex.  Rather, they are computed on the fly by the EVE servers, to attempt to keep things together that are currently on the same grid.  A grid will be stretched, amoeba-like, if a ship is moving to its edge and there is no other grid already in that direction.  (This process can be manipulated by players; look up "grid-fu" sometime.)  For our purposes, all you need to know is that most objects show on your overview only when on grid.  This includes ships, wormholes, wrecks, cans, and POSes.  It does not include gates, customs offices, and stations -- these appear on your overview regardless of grid.  So, to make an off-grid bookmark, identify any object on grid which cannot be seen off-grid.  (If there is none, make a jetcan.)  Then move away from object until it disappears off your overview.  When that happens, you are off-grid, at least right now.  Note that if you want to use the bookmark indefinitely as an off-grid perch, you should make it more than 300km from the target, because future grids may not be congruent with present ones. 700-1000km is good.

Examples of Use

The classic situation in wspace is a sleeper wreck field.  If you find one of these, you can expect a salvager to come along eventually.   If you can get on its grid in a stealth bomber or cloaky T3, you may get a good gank target.  However, until the salvager enters the site you don't know where it will be, exactly.  So you create a perch that is at least 150km from all the wrecks.  Because you can warp to wrecks (so long as they are not being tractored), and cans, you will have a variety of points to warp to, so that you can quickly be at a variety of locations.

In kspace, a classic situation is a gate in null.  Gates can be camped, and in null this means bubbles.  You don't want to fly into a bubble with a non-cloaky ship, and be trapped by it.  But bubbles only affect ships that warp on to their grid.  So, for each gate in a path you want to use, create an off-grid perch.  Now you can fly non-cloakable ships with reasonable safety.  Never warp directly to any gate if there is anyone other than you in local.  Instead, warp to your perch near that gate, and dscan the gate to see if there are any bubbles and/or campers.  Then you can decide whether to proceed.