In his poem "London," William Blake refers to the streets of London, and to the river, as being "charter'd." This could have several meanings: first of all, a chartered street is one that has been recorded and written on a map and is part of the official layout of a city. The streets are chartered in that they are registered and are approved by the local government and by the people in authority.

Of course, there is an inherent criticism here. Blake goes on to discuss the "woe" in the faces of everyone he meets, all of whom are filled with fear and whose minds seem to have been locked down with "manacles." A comparison is drawn between the streets of the city, which are bound to follow the routes written down in the maps, and the minds of its people, who are likewise unable to think beyond what they have been told to think.

The point that Blake is making is that London is a city that is too bound to its historic strictures, even though the result of those strictures is actually widespread poverty and bloodshed. He is criticizing the fact that too many people in London are forced to adhere to rules and live within the guidelines of a society that does nothing for them.

In the first stanza of this poem, the speaker seems restless, wandering through the streets of London near the banks of the river Thames. As he looks at the faces of those people he passes, he sees their sadness and their pain. This seems to suggest some link between the "charter'd street[s]," "charter'd Thames," and the depressed and miserable people of the city. This is further affirmed by the second stanza's reference to the "mind-forg'd manacles" worn by the people of London: the chimney sweeps, the soldiers, the prostitutes, and even the babies and the church-goers suggested by the third and fourth stanzas.

Thus, the word "charter'd" (in lines one and two) seems to suggest both confinement and having been mapped out (like how we might think of "charted territory"—land that has been mapped out). The streets and river seem to enclose or confine the people of the city, where their roles and lives have been "charter'd," or mapped out for them, so that they lack real freedom or possibility. The speaker says that "each [...] street" is "charter'd," suggesting the idea that, in the city, there are no places where there is room for imagination, nature, fantasy, or possibility. Everything is determined, regulated, and bounded, compounding the misery of the inhabitants and their sad lives, which inevitably continue in this way until they end up in the "hearse" of the final line.

In the first two lines of “London,” Blake wanders through “charter'd” streets near the “charter'd” River Thames. In literal terms, the streets and the river have been chartered or mapped. They also form barriers of one kind or another; the streets are an artificial barrier, whereas the Thames is a natural one.

But it's the figurative meaning of the word “charter'd” that's important here. The physical barriers presented by the streets and the River Thames are outward symbols of the “mind-forg'd manacles,” those mental barriers that keep the people of London in a state of oppression.

As well as dealing with physical barriers, both natural and man-made, the people of London have to deal with a narrow mindset that keeps them intellectually crabbed and confined. Such narrow intellectual horizons make the people of London vulnerable to political repression and subjugation by the authorities, both secular and clerical.

The powers-that-be rely on the minds of the masses remaining “charter'd” in both senses of the word as Blake uses them. They are “charter'd” in that they can easily be mapped and measured, making it possible for those in positions of power and authority to control them. And their minds are also “charter'd” in the sense that they are confined to a specific locale, trapped as the common people are by poverty and degradation.

To me, this word is used twice in the first two lines to emphasize the theme of the poem.  The word itself has a couple of possible meanings:

First, I believe the word refers to the idea of charters.  These were agreements that were written up (sort of like contracts) that spelled out the rights a city or a guild or something had.

Second, I believe it refers to the idea of charts, or maps.

In both cases, the idea here is that the streets and the rivers have been heavily influenced by people.  They have been mapped out and they have been subjected to rules (charters).  They are no longer in any way "free."

This goes along with the main theme of the poem, which is that city life has taken away the freedom and vitality of the people and has oppressed them.