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Warp space is a realm capable of navigation but, at least in the scope of human knowledge, a mysterious phenomenon. There is some evidence that transdimensional rifts occur between warp space and the material universe spontaneously, though data are limited. While such rifts can be created artificially, warp travel should not be undertaken lightly. If co-ordinates aren't plotted correctly, a ship's crew can end up dead and/or so far from their intended location that they can never get back.
In addition to travel, warp space also provides a means for transmissions to be sent in real time, able to even be received in warp space or in the case of the zerg and protoss, via long distance telepathy. It should be noted however, that each species' usage of warp space is not on an equal level:
Terrans developed warp engines by the 23rd century, which allowed the colonization of the Solar System, travel to further star systems (coupled with cryogenic hibernation) and eventually travel to the Koprulu Sector. Upon their botched landing, the exiled terrans had to redesign warp travel (it took them sixty years to redevelop subwarp engines using information taken from the ATLAS).
Terran jumps through warp space can be short ranged or long range, the latter being reserved for large ships such as battlecruisers. For these jumps, a few hours are required to charge up the engines, along with plotting the co-ordinates. A long jump can be made instantly in desperate circumstances, but this is regarded as extremely hazardous. Still, when properly planned, these jumps can be highly accurate, terran technology being sophisticated enough for one ship to warp right in front of another. Terran vessels "leap" through warp space, making it very difficult to track a vessel's course from the direction it is facing. Potentially compounding issues is that terran vessels can't detect objects (e.g. enemy forces in real-space) while in warp, allowing them to drop into hot-zones without warning. For instance, terran technology is sophisticated enough for capital ships (such as the troopship) to emerge from warp space one planetary diameter away from the host planet. During the Guild Wars however, three planetary diameters was used.
Terran warp space travel also has to bear with a number of other considerations. A ship should not re-enter real space too close to a planet and must have a clear line of movement to make the jump (a ship positioning itself in front of a target vessel will prevent the target from jumping; a useful tactic in space combat). It should be noted though that the Hyperion seems to be able to enter warp space from a planetary surface. Finally, warp travel can be exhausting, as the mind is unable to keep up with the extreme speeds that the body is moving at. On exceptionally long journeys, cryogenic hibernation is used.
There is a visible distortion in the fabric of real-space when a terran vessel exits warp space (or at least vessels the size of battlecruisers).
It should be noted that these characteristics apply to the level of terran technology in the Koprulu Sector and not to that of the United Earth Directorate, whose technology is (theoretically) more advanced. At the least, the UED was able to make a 60,000 light year trip to the Koprulu Sector in less than a year in 2500 whereas it had taken the original supercarriers 28 years to do so in the original colonization mission.
Despite being a race with no use for technology, the zerg still maintain the ability to travel through warp space, as they can open large gateways into warp space. The power of these gateways was immense, able to even pull zerg off the surface of a planet, emerging at their destination. This process was highly accurate, the zerg emerging right over a planet, so accurate in fact, that it appears the zerg could enter real space within a planet's atmosphere, as no traces of atmospheric entry (eg. a buildup of heat due to friction) ever being observed. The Overmind had the ability to open these warp rifts, as did Kerrigan.
The protoss have spent thousands of years studying the nature of time and space and as a result, their ability to manipulate it far exceeds that of other races. Protoss ships are able to enter real space far closer to celestial bodies than terran craft and are able to enter warp space far more subtly, seemingly "disappearing".
In addition, the protoss are capable of opening warp space rifts even on the surface of a planet, courtesy of warp beacons. Through tapping in to the psionic matrix provided by a nexus, protoss are able to warp structures, constructs, warships and even infantry onto a planetary body and if required, an entire base may be warped via "dimensional recall", though this requires an extended period of time (at least thirty minutes).
The xel'naga were a technologically advanced race and while little is known of them, it is apparent that they possessed the ability to travel through warp space, courtesy of warp gates. However, their ships were also capable of traveling through the void. The xel'naga possessed the ability to travel between galaxies.
The song I Can't Drive Warp 5.5 may indicate some kind of 'warp factor' system existing for warp space travel, at least for terrans.