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.
Chartered suggests the privilege of those who can hire the river Thames itself for their use and whose lives contrast with the misery of the poor. It also suggests that all of this is charted (i.e., mapped), and thus the city itself has violated natural beauty by creating artificial streets, and by consigning even the river to commerce and ownership. Other words suggest this same theme and suggest that "Marks" in line 4 means permanent marring of people’s faces by grief; in line 3 it simply means observe. In stanza four, the reiteration of the bl- sound gives each word emphasis, as does the position of this sound in stressed syllables. These words use the foundation of chartered to build Blake's vision of London.
The poem is about what a miserable place London has become. "Chartered" means controlled. "Chartered Thames"- Even nature is controlled by the leaders of the country. People have no freedom. The man-made streets are controlled. So is Nature. ..The River is ''Chartered".
It can also mean metaphorically polluted by corruption. There is political corruption and even the church is "blackened" -and the citizens are unhappy.
In my opinion the poet narrated that the king considered the country as his own properties " chartered street and chartered Thames". Chartered means document by corporation,the chartered were given by government and nobody has a right to use them .