The earliest map of the entire city of Dunwall that we see is the map published during the reign of Lord Regent Hiram Burrows. Since it bears the Lord Regent's livery it must have been published in 1837, although the survey work was probably completed before that. Most importantly, it provides us with some dimensions and statistical information about the Imperial capital.
City Of Dunwall
In the real world, the 'City Of London' is no more than a square mile in size. This is because what we commonly call 'London' is actually multiple town and county councils within a single contiguous urban area. I imagine something similar is at work in The Isles: Dunwall is a single large urban area, but the Lord Regent's map of 1837 probably only displays 'Greater Dunwall'.
Maps of The Isles usually have a scale diagram, but these only contain numbers and never units. This is one reason the Lord Regent's map is so important: it clearly gives an area reading in square miles. By observing the size of the markers along the borders we can determine the map's proportions. A little geometry and algebra allow us to determine that Greater Dunwall is about 3.4 miles wide (east-west) and 5.7 miles long (north-south).
15 Years Later
Compare the Lord Regent's map with what I'm calling the Amelian Map, which is the definitive Dunwall map in 1852 during the reign of Empress Emily I Kaldwin. The Amelian Map clearly covers a slightly larger area (we can see more of the islands in the river, for example) but without knowing the exact area it covers I'm not comfortable making an estimate of the dimensions.
Look carefully at the Amelian Map and you will see Dunwall has changed significantly. The railway network has been expanded, streets don't always follow the same path, and more bridges now span the Wrenhaven.
Bridges & Crossings
We know that the small rubble depicted going across the river from the Distillery District to the Drapers' Ward is a ruined stone bridge, as we saw it depicted in the first Dishonored. Look carefully at the Lord Regent's map and you will see there are other ruined stone bridges: another next to the Distillery-Drapers bridge, one between the Distillery-Drapers bridge and Kaldwin's Bridge, one adjacent to Dunwall Tower, and one just past the Old Hound Pits Pub. These ruins may be present but they do not obstruct shipping, since we have seen whaling ships traverse the Wrenhaven from its mouth past Dunwall Tower and into Slaughterhouse Row past the islands in the river (hereafter the North-West and South-East Wrenhaven Islands since I have no better name).
Now look at the Amelian Map again. One of the bridges from the Distillery District have been repaired, a new bridge has been installed half-way between the Distillery Bridge and Kaldwin's Bridge (though the original ruins are still there), and Wrenhaven Island is now connected to the mainland by two bridges. One Wrenhaven bridge connects it with Holger Square, the other is a railway bridge that spans the entire river.
I'm going to be referring to these old, new and ruined bridges quite often so I'll quickly give them some unofficial names.
|Holger Bridge||Connects North-West Wrenhaven Island with Holger Square|
|Wrenbridge||Railway bridge connecting both sides of the river via South-East Wrenhaven Island|
|Half Bridge||Ruined bridge going east from the Distillery District but stops half-way through the river|
|Old Bridge||Ruined bridge going east from the Distiller District and 'connects' the mainland. This is only depicted in the Lord Regent's Map.|
|New Bridge||Repaired bridge going east from the Distiller District and connects the mainland. This is only depicted in the Amelian Map.|
|Old Waterloo Bridge||Ruined bridge going half-way across the river, half-way between Old Bridge and Kaldwin's Bridge.|
|New Waterloo Bridge||Complete bridge going half-way across the river, half-way between Old Bridge and Kaldwin's Bridge. This is only depicted in the Amelian Map. (Named because it connects the old waterfront.)|
|Tower Bridge||Ruined bridge that passes beside Dunwall Tower|
|Rudshore Bridge||Ruined bridge going east from Rudshore but stops half-way through the river. This is only depicted in the Lord Regent's Map.|
There's some interesting trivia to be discovered in studying these bridges.
- In the Lord Regent's Map, only Kaldwin's Bridge completely spans the river; all other bridges are depicted as ruined.
- In the Amelian Map there are four new crossings: Holger Bridge, Wrenbridge, New Bridge and New Waterloo Bridge. Only New Bridge has been rebuilt over existing ruins, the rest are utterly new bridges.
- In the Amelian Map the ruins of Half Bridge, Old Waterloo Bridge and Tower Bridge are still depicted. Rudshore Bridge is absent.
The Single Crossing Of Kaldwin's Bridge
In 1837 only Kaldwin's Bridge completely spans the Wrenhaven River. This indicates all the other bridges collapsed or in the distant past. Evidence seems to point to the former: according to an in-universe book (deleted from the game) Kaldwin's Bridge replaced an existing crossing that had been built using pre-Whale Oil technology. If engineers could bridge the 10 000 ft -ish span of the Wrenhaven at its widest point, they would certainly have built lesser bridges at other points -- especially since bridges are critical for cities like Dunwall.
So why weren't the bridges still there in 1837? Well, Dunwall had been cutting maintenance corners for the Rudshore Dykes since 1826, though the disastrous results were only felt ten years later. Perhaps this same disregard for upkeep left the stone bridges critically fragile. If Rudshore's Dykes broke during a hurricane or similar natural disaster, the bridges would also have been swept away. The greater destruction in Rudshore would have gained more public attention than the relatively simple loss of a few bridges. And good luck trying to find the labour to repair them with the Rat Plague in full swing!
Types Of Bridges
Kaldwin's Bridge is a drawbridge and is depicted with large pylons and a wider span than the other crossings in the Amelian Map. There are only a few pylons on Wrenbridge, perhaps indicating a cantilever or suspension/stayed bridge. New Bridge and New Waterloo Bridge have more frequent pylons, which may indicate a conventional arched viaduct style bridge. Alternatively, New Bridge and New Waterloo Bridge could also be cantilever or suspension bridges; Wrenbridge was simply the last of the bridges completed, allowing engineers to push the limits of the technology.
Clearing The Ruins
The ruins of Rudshore Bridge have been removed in the Amelian Map. This perhaps indicates that clearing the Flooded District required the dredging of debris along that part of the river, in order to build a stable foundation for the new Dykes.