Sector
In cartography, a sector was an area in physical space. 

The surface of planetary bodies were gridded into sectors. (; )

In stellar cartography, a sector, which was referred to as a star sector or space sector, was a gridded region within the Milky Way Galaxy. Sectors were composed of an area and volume encompassing several light years and typically contained several star systems. A group of sectors was called a sector block, which was located in a quadrant. The sector system and their numbering was used by United Earth, Vulcans, and other spacefaring races at least by the 22nd century. In 2369, the extragalactic space was not divided into sectors, and ships that were sent on deep space cartography missions were listed as being in extragalactic space. (; ; )

Size and range 

William T. Riker felt that the warp coil was perhaps one of the greatest advances in Humanity since the 22nd century, explaining that "before there was warp drive, Humans were confined to one sector of the galaxy." ()

When the  was probed while en route through an unfamiliar sector of space in 2269, the crew was able to determine the source as being from a planet in the Taurean system, a system located twenty light years away, at the extreme edge of their sector. ()

In preparation for Operation Lovely Angel, the  scanned all sectors located within three light years of the Oneamisu sector. ()

A  ship was capable of scanning a radius of ten light years at a time, which allowed the ship to effectively scan one sector per day. ()

While en route to the planet Barisa Prime in 2371, Captain Benjamin Sisko noted that the closest ship in that sector, the , which was exploring the Helaspont Nebula, was located twenty hours away at maximum warp. ()

The territory occupied by the Swarm species covered "a huge area of space" and included "hundreds of sectors." For the  to go around that region, it would have taken over fifteen months at maximum warp. ()

Voyagers use of Tash's catapult "hurtled" the ship across thirty sectors of space in less than an hour, a journey that would have otherwise taken three years to accomplish. ()

Composition

Sector Z-6 encompassed both Federation and Romulan space, and during the 23rd century, included seven Earth Outpost Stations, the Romulan Neutral Zone, and Romulus and Romii. ()

The sector containing the quasar Murasaki 312 contained at least four complete solar systems. () 

The sector containing the planet Iconia contained three systems whose inhabitants had several cultural similarities with the Iconians. ()

The sector in which the Enterprise-D intercepted the class 8 probe occupied by Ambassador K'Ehleyr was said to contain very little, yet included four colonies and nine outposts throughout. A nearby sector that was threatened by the Klingon sleeper ship  contained thirteen Federation colonies. ()

When the shuttlecraft  achieved warp 10, it collected data describing "literally every cubic centimeter" of the sector they were in – an amount of information exceeding five billion gigaquads. ()

Naming
Most sectors were numbered, and in some cases, named after an important star system in that sector. In Federation nomenclature, the Sol system and Earth were located in Sector 001. () Others were named after a key star system, such as the Mutara sector. () In other cases, they were given a designation consisting of both a name and number, such as Rhomboid Dronegar Sector 006. ()

Subsector
A subsector was a region of space smaller than a sector and located within sectors. Subsectors were also numbered, for example Subsectors 4534-4432 within sector 450/32450 ( display graphic) and subsector ref 321-053 within sector 30-489. 

The latter number, such as the 053 in subsector ref 321-053, was the angle at which the subsector was being viewed on screen. ( display graphic)

List of sectors
 See List of sectors
 Unnamed sectors

Background Information
The  defined a sector as, "In interstellar mapping, a volume of space approximately twenty light-years across. A typical sector in Federation space will contain about 6 to 10 star systems, although sectors toward the galactic core will often contain many more. The Milky Way Galaxy is divided into hundreds of thousands of sectors, grouped into four quadrants. Sectors are usually numbered, although in common usage they are often named for a major star or planet located in that sector."

The Star Trek Encyclopedia (3rd ed., p. 434) authors additionally said,"The numbering system for sectors had been inconsistently used (and sometimes interchanged with quadrants) during the show, especially in its early days. We assume that some sectors may retain older designations from previous mapping systems, much as present-day astronomers still use NGC and Messier catalog numbers."
 
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Cartography