In the play's opening scene, King Henry remarks that his messenger's horse has been "stain'd with the variation of each soil" as it travelled from Northumberland to London to deliver news of a battle in northern England (1.1.3). This vivid depiction of the soil-stained horse captures perfectly the play's interest in covering a broad geographical range (on a single stage, we might add, which is very impressive). Check out this nifty map if you need a visual of Britain.
Henry IV Part 1 is set in England and Wales around 1492 and portrays diverse locales – the king's palace in London, various fields of battle, the seedy Boar's Head Tavern in London's Eastcheap neighborhood, the mysterious and sensual home of Welsh rebel, Owen Glendower, and so on. That's a lot to cover, so let's get busy.
The royal palace in London is where the king hangs out, makes decisions about important state matters, and lays into his rebellious subjects and his unruly son, Prince Hal. The vibe here is grave and serious, so much so that Hal feels the need to have a kind of dress rehearsal before his confrontation with his father.
The infamous Boar's Head Tavern, on the other hand, is a dive bar in London's Eastcheap neighborhood. (Even though the play's set around 1492, critics like Jean E. Howard note that Eastcheap looks and feels a lot like England's colorful commercial district in the 1590s. Here, notes Howard, characters drink imported sweet wine, refer to clothing worn by Elizabethans, and make fun of popular Elizabethan plays.) This is where Hal cuts loose with his buddies and hangs with the commoners.
Aside from being a really fun and colorful hangout, the Boar's Head is an important location because it's a space where matters of state are made fun of. In the famous play-acting scene, Prince Hal and Falstaff turn the tavern into a mock "palace" and take turns performing the role of "King Henry," which is a pretty rebellious thing to do. This rebellious act is also something Elizabethan actors did every time they took the stage in a performance of King Henry IV, which makes the Boar's Head Tavern seem a lot like a rowdy theater. (You can read more about this by checking out "Art and Culture.")
Gads Hill is the location (on the road to London) where Falstaff and his crew rob the king's exchequer (treasury) just before Prince Hal and Poins jump out of the bushes and rob Falstaff, who barely puts up a fight before retreating like a coward. The setting and the robbery can be seen as a comedic parody of what will later occur on the battlefield at Shrewsbury.
Battlefields are significant places where "honour" is won and lost. At Holmedon, Hotspur takes important prisoners, defeats the Scottish invaders, and gathers many "proud titles." Later, at the battle at Shrewsbury, Prince Hal kills Hotspur, taking all of young Percy's "honours" for his own. For Hal, then, the battlefield is a place for redemption and transformation. It's where his father forgives him for his wild behavior and also where Hal begins to pull away from Falstaff and his "vile" ways. Falstaff, on the other hand, treats the battlefield at Shrewsbury like any other one of his stomping grounds. This is where he plays dead like a coward and lies about killing Hotspur, all of which recalls the comedic episode at Gads Hill, where he also behaves like a coward.
While most of the action takes place in England, a few scenes occur in Wales, at the residence of Owen Glendower. In the play, Wales is associated with "wildness" and mystery, despite being right next door to England. It's also a dangerous place, where Glendower is said to participate in black magic, where the rebels convene and make plans to divide the kingdom into three parts, and where Mortimer turns traitor and lolls around in the lap of his new Welsh wife. In the play's first act, we also learn that 1,000 English soldiers have been slaughtered in Wales and their bodies mutilated by the Welshwomen. The play suggests this isn't a place where Englishmen want to get caught. The portrayal of Wales is pretty unfair and speaks volumes about Elizabethan attitudes toward the Welsh.