Quoting myself from another forum I posted those two maps and was asked about backgroud:
The Bloodmarch Region is pretty nondescript, outside of containing an Astartes Homeworld.
Subsector Hel honors it's name by mostly being one engine of war continuously trying to fend off a Daemon Incursion from the Absum Coepi Breach, which basically is a tiny breach in realspace into the Immaterium. Lots of soldiers thrown into the Demon War there, including most of the Bloodknights Chapter.
Subsector Yrean is dealing with a big-ass revolt that has been going on for a while. Yrean (the world) and Kravicz remain of the three original revolutionary worlds. Guuti was ended for the same reasons, and Yrean is quickly loosing in value as well. If the war continues for another half a decade Exterminatus will be considered no matter the manufactories on-planet.
Subsector Calidas is the bread-basket of the whole Sector, due to Pharis' Bounty, a string of extremely valuable and rich Agriworlds that supply enough food to keep most of the sector's Hiveworlds fed. Nymak Celo and Novus Bellus belong to the Bounty as well and are two extremely beautiful planets that are kept as garden/pleasure planets.
The Prometheum Reaches are an extremely valuable region that keeps the sector at large stocked with ressources. High-yield Prometheum and Mining worlds abound. Only problems is the tendrils of Behemoth's Calidas Hive Fleet are slowly moving into the subsector and threatening the worlds here. Around a century ago both Rhavak and Meneghast have been turned into fortress worlds in anticipation of the threat. A large-scale naval engagement under Admiral Toulan defeated the vangaurd of the hive fleet in the outer reaches of Rhavak in 916M41 here. This might keep the Hive Fleet away from the highly important ressource worlds for a little while longer.
Subsector Colmaris is the population center of the whole Sector, due to it's four enormous Hiveworlds. The Subsector also sees regular Eldar activity. To the right of Subsector Colmaris you can find the Burning Wrath Nebula Anomaly, which was spotted only after Hollow and Dread had been settled. The nebula expands in enormous bouts, swalling worlds and systems wholesale. Nobody has ventured into the anomly and returned so far.
The Danica Cluster has been designated as staging grounds for most military operations against the Hive Fleet, with Kurox III being assinged specifically to house the Hyrion Sector Battlefleet that was sent here to support the Anti-Tyranid movements. Mixed Eldar and Genestealer activity has the higher-ups worried, esp. since Eldar activity picked up enormously with the arrival of the Battlefleet Hyrion.
Subsector Anduun is named after a Shrineworld dedicated to - you guessed it - Anduun the Sainted, whose story I never quite fleshed out. The gist of it was that a large-scale rebellion broke out and the Saint fought valianlty against the enemies of the Imperium for many decades. The Rebellion is also responsible for the Subsector basically going to hell: Ortis' Folly, Mieros and Elok Artis have been Exterminated due to rebellions. Penitence and Betrayal have become forbidden worlds for no explanation at all, and Fered's Star became a Fortress World in this conflict. Istvan XI was designated Fortress World as well later down the line, when the Behemoth Tendril became stronger and stronger. Even though much work flowed into Istvan XI, the Tyranids simply ignored the planet and went to either side of it.
Anduun also suffers from a massive four-front war between Imperium, Orks, Tyranids and Eldar.
As if this wasn't enough, the Tau have expanded into the area slowly, and promise more problems down the line - if there is a down the line for this Subsector.
Subsector Bitas is currently one of the main fronts of battle against the spreading menace of the Tyranids. Isos has been Exterminated after the Tyranids were close to overwhelming the planet, while Fogh remains a thorn in the side of the Hive Fleet, ever defying the Tyranids... so far, at least. Bitas, though, right behind Fogh, has been decoured in full. The Subsector is doomed, and all the Imperium can hope to do here is cut their losses and inflict as much damage on the Tyranids as they possibly can.
Subsector Volok is about to engage with the Tyranid threat, with Gregoris being the focal point in military action here. The Hive Fleet was already spotted in Alaides over a decade ago, but the Eldar did something, and the Hive Fleet's vanguard disappeared or retreatet - the Imperium is unsure which of both.
Subsector Rigor is dead. Before it's fall the Subsector was a mix of Imperial Worlds and some industrial things. Subsector Kessel is equally-dead and is home to the greatest shame of the navy in this region, Gadrian's Defeat in 877M41, where the Admiral ordered the Battlefleet Calidas to engage a Tyranid Vanguard. The Vanguard was soon reinforced by enormous bioships in the dozens, until the Battlefleet suffered a catastrophic loss in the face of Admiral Gardian's refusal to retreat. The remains of Battlefleet Calidas are being repaired and brought back into service, while Battlefleet Hyrion is taking over a lot of the work.
Subsector Caiphas was created before I ever heared of Ciaphas Cain, btw. It's a major reason for the strength of the Tyranid Hivefleet, since many of the outlier worlds (Asuraya, Tiranis, Alebar) were devoured without much resistance. Imperial Forces were engaged otherwise at the time and the threat of the Calidas Tendril stayed quite for some time for Emperor knows what reason.
A couple other points: Exis, between Hel and Calidas Subsectors, is a world lost in 873. Contact broke off completely and when scouts checked on them, they found the planet devoid of life.
Ghurdan and Zhovokhaz are the two Frontier Worlds that were supposed to be the founding-stock of a new Subsector. Bad for them that they chose Necron turf and did awaken some of the seemingly mindless machines whilst digging in the icecaps for valuable materials. Both worlds were depopulated quickly and scouts sent to the region never returned. At this time the Tyranid Hivefleet became more and more dangerous and attempts to colonize were shelved in favor of more active measures agains tthe Tyranids.
Between Subsector Bitas, Kessel and Volok one can find the Karex Formation, three unclassified worlds that are avoided by Eldar, Imperium and Tyranid alike for no apparent reasons.
Okay, half of this was made up on the spot just now, but it's kind of the vibe I have for Calidas. Hope you enjoyed it.
Set on the outermost fringes of the Ultimar Segmentum, the Karsus Sector borders on the Fading of the Astronomicon, where the Light of the Emperor becomes so slight that navigation becomes nearly impossible. The primary threats in the region are the Chaos Incursions in the Red Haze, an Ork Waaagh! in Kendra's Expanse, and Blake's Realm, a region of space regularly impassable by warp for centuries at a time, thus leading to rebellious spirits rising.
A quick tour thorugh the subsectors, then...
The Fire-Belt is named so for it's many Prometheum-rich worlds and the fact that most of them are infernal worlds with temperatures well outside of 100°C or more. Survival on these planets is harsh and only possible through large self-sufficient complexes maintained by the Adeptus Mechanicus. Closer to the Red Haze, Tsaino and Klammach see regular Eldar activity, and imperial forces have clashed on the planet more than once. After a larger engagement involving significant forces that hint towards a nearby Craftworld, the Imperium decided to leave the Eldar to their business, as they kept mostly to places on the planet where no Imperial facility was nearby. Red Gate, the Subsector Capital, sends regular scouting groups and stands ready for a full large-scale engagement.
Subsector Oldenburg is dealing with two smaller Ork resurgences on Khirad and Tochin, Frontier Worlds each. The local militia is having problems, and the Guard has been called in, even though they are already occupied in Kendra's Expanse.
Subsector Faroe is home to several Dead Worlds, the valuable Gurthman System and Alto, a Forgeworld renowned for it's production of Plasma Weaponry. Ignar, Blochert and Thylon - the Dead Worlds - were destroyed in intercenine warfare, a brothers-war that spanned all three systems and ended in commensurate nuclear terminator on all sides. The planets are highly irradiated, and officials decided that most of the valuable ressources had been stripped from the planets anyways.
The Gurthman System consists of two Industrial Worlds that output enough materials and common items to supply a larger Subsector all by themselves. The worlds have a proud industrial tradition that can be reminiscent of religious zeal or fervor.
Subsector Gordaine is a bountiful region of space, sporting four valuable Agriworlds that supply most of the Fire-Belt and the local Hiveworlds. In recent years several planets (Halbrook, Tsagen, Stille and Relick) have shown clear signs of rebellion and dissent, later found out to be the work of Stealer Cults. The situation is still heating up, and according to official sources the Emperor's Angels are due to arrive soon.
Gordaine also contains the six unclassified worlds that seemingly reject anyone wanting to examinate them. Seven different expeditions were sent there to evaluate the systems, and each returned with wildly different readings, devianting in the extreme.
The Forge is the beating heart of the Karsus Sector, an industrial Juggernaut so enormous that it supplies not just this Sector, but many others as well. Goods flow from The Forge in unimaginable quantities, in no small part due to the Arxus Forgeworlds and the nine Industrial Worlds in the Subsector. The demand for workforce is so enormous that regular ferries from the local hiveworlds and the Hiveworlds Subsector bring in new workers and ferry others back home after excrutiating weeks of near-constant work.
In addition to the Industial Worlds and the Arxus Forgeworlds the Subsector also features the well-known Korvus Yards, an industrial Juggernaut all in itself, capable of producing over two dozen ships at the same time, it's constant hunger for material fed by the immense industrial capacity of The Forge itself.
The only major problem The Forge really has are the worlds of Blaze, Gurdum, Virkan, Hellestin and Igari, all of which are now Forbidden Planets. Enormous hordes of Orks once ravaged these worlds, a war so fierce that many of Arxus' Collegia Titanica sections were mobilized to these worlds. Now that the Ork presence has been negated, the worlds are barren husks, but still promising. First endeavours to re-colonize these worlds are slowly shifting into gear.
Myria's Blessing is the complementary Subsector that keeps The Forge fed. The Forge's insane industrial capacity would not be possible without food, but thanks due this region, kept safe by Saint Myria in the past, things work hand in hand to keep everything running.
Havart's Rebellion was the first world to feel the effects of the Strife Winds, a strange anomaly that seems to make people desire more freedom than would ever be sane. The strange ethereal radiations from this anomaly have caused much problems, and following a full-scale uprising, the world was turned into a Penal Colony where no quarter is given and everyone not obeying every word of the Wardens will be shot that very same instant.
Kendra's Expanse was the focal point of the Only War campaign. Two major military engagements are ongoing here. Kain's Nebula is a nebula that suffers intermittent warp-storms that cut off all contact for centuries at a time. This naturally leads to deviation from the Imperial Creed and as has often been the case, when re-emerging and coming into contact with the Imperium once more, the region has taken up a banner of independence. Currently the region is under rule from a mysterious character only known as "Blake", a person inspiring fierce loyalty among subjects.
Blake's Realm is now the subject of the 3rd Kendra Crusade, it's staging ground being Tresitas.
The second big problem is a major Ork Waaagh that so far holds five worlds in it's strangulating grip. Only a couple years ago has the Ork threat been classified as strong enough to warrant inclusion in the 3rd Kendra Crusade, with it's staging-point being Brandt. Part of the Orc-Situation is also KX-8, a planet closely guarded by Eldar forces.
A quick note here: Katwa was the planet our Only War campaign was going on. I used the adventure in the back of the Core Book to start off the 11th Krimean Drop Troopers.
The Hiveworlds Subsector contains an inordinate amount of Hive Worlds - Thus the name. The subsector is utterly dependent on others for survival, due to not boasting even one Agriworld. On the other hand, the Subsector contains Thundersky, a strange world in it's own right, due to the Stormleash Anomaly that plagues this subsector and the Leash Subsector. The Anomaly consists of bands of elctricity and agitated particles slowly winding their way through space. The tendrils of the anomaly tend to suddenly lash around like a whipe or leash (thus the name) and have more than once bured a planet clean of life, notably Rho-5 and more recently Edena, which was turned into a Death-World by contact with the anomaly.
Thundersky harnesses some of the Anomaly's powers. The system is embroiled in strong storms and the planets atmosphere is charged with electricity. Thanks due to the Adeptus Mechanicus, the planets manofactoiums are powered by these storms and require no other power-source.
The Subsector is also home to Azure Sky, Homeworld to the Storm Hawk Chapter of the Adeptus Astartes.
The Leash Subsector is primarily interesting due to Kalyxos, a major space-station used to analzye the Stormleash Anomaly and Krim, a Death-World renowned for it's hard people and the recetn First Founding for new Imperial Guard Regiments, primarily consisting of Drop Troopers, Light Infantry, Hunter-Killers and Scouts. The characters from my Only War campaign started here.
The Subsector Kattaral has it's own share of problems, since a major Ork Waaagh! is shaping up here. Many worlds have fallen to the beasts by now, two of them having been Exterminated to spare the population the gruesome death by slavery. After Isvald falls, the orks will have a major fortress ahead of them: Kattaral. Backed by the Port Imperius Shipyards, the Fortress World is exptected to hold the Orks back until additional troops can be brought in to stem the green tide.
Subsector Gallatus is a slowly expanding Subsector that currently maintains a handful of Frontier Worlds. The problem of Subsector Gallatus is the Mortax System, in which strange xenos warships move about (hint: dem necrons!).
Lastly we have the Forlorn Reaches, named aptly so due to the proximity to the Fading of the Astronomicon. Many dead or dying planets are scattered here and the only real worlds of note here are Cathil and Doyle. Everything else is death, despair and bleak worlds at the edge of Imperial space.
Once again, half of this stuff is made up on the spot, but fits the image I have.