A very interesting phenomenon happens in 18th century London. It happens everyday and it transforms the city. Night. Every evening the place London changes its space, as day turning into "The Evening" is described by Gay at the start of Book III:
Helpful signs on shops during the day become threats at night, capable of striking the London walkers as they close. This is why Gay gives us a poem on "How to walk clean by Day, and safe by Night" - not just simply how to walk in London (at any time). London's nocturnal space differs socially from the diurnal London of Book II. Sven Armens (John Gay: Social Critic) informs that the poem is, "evocative of two very different moods; the bustle and cries of crowds as the shops open in the morning to the sound of trundling carts; and the sinister play of shadows about the "common-shores" at night when the street lantern has been blown out" (76). [See pp 75-76].
This cyclic change in Gay changes walking "clean by day" into "safe by night" - the same space in day, which is only hilariously or marginally dangerous (against the man in a chair, or the coach driver) becomes dangerously dangerous at night. Books I & II are concerned mostly with those "Beaus" that do not want to get their "boots dirty." The first two parts of the poem are about how to stay clean in the day. In the night time it becomes far more nefarious; it is necessary to "walk safe;" it becomes a space in which one must avoid walking i.e. the square that is only inconvenient in the day. At night you run the risk of being robbed and attacked.
The down-town London urban pastoral space represented in the day becomes a Foucaultian heterotopia at night. In the section glossed "The Danger of Crossing a Square by Night" we have:
The inconvenience of the day's begger turns into the danger of the night's thief. The Square, then, becomes a heterotopia because it is profaned and to be avoided, but only temporally.
The night time spaces are day time places transformed, i.e. Lincolns Inn. But how do we map this? They exist on the exact same physical place, yet because of their differing temporalality, they are different spaces. Because the place is the same, i.e. the literal physical space, one physical (or digital representation of a physical) map should be used to help the reader understand visually that it is the exact same setting. The digital "post-modern" approach to post two visual aids side by side should be resisted - for the moment - so we can see the two different temporal spaces on an identical place; we want to conflate these two spaces into one place:
The same map must represent dual temporal spaces. WIthout getting into 3-dimensional modelling or animation, a simple solution is to mark the locations or spaces by day in white background with black tag, and the ones at night in the opposite, black background with white spaces. Thus, on the same physicality we have marked two temporalities, just as Gay attemps to do in Trivia's London.
Still resisting the urge to display two maps side-by-each, another way to view night and day at once is by displaying only night or only day tags at once. This is probably possible to do using a more advanced "show/hide" tags feature, but the way I will accomplish this is to use to use a php switcher (and in this case, a screen shot of the map with day or with night tags) to view the different tages at differing times. Thus, for each screenshot we will be be vewing the space at a certain time, not as an amalgamation of space-time:
This website shows dual-mapping techniques as a "micromapping" approach: the exact same spot is mapped twice for two different times. This approach could encompass all of London, with "night" tags and "day" tags. In a grander scheme, more than two tags could be applied, and each label could have several "tags," which, through a more complex system, would allow for complex search queries: only "women" at "night" who are "pedestrians" or, only "men" during "day" that were "car-men," etc. In this way, the digital map becomes necessary: it is no longer something possible to achieve in print.
The importance of the "different space in identical place" approach, i.e. using the same map, becomes an effective tool only when it comes to generally cyclic or otherwise vacillating spaces. In a previous presentation, I put for the idea of the changing political space of Smithfield Park over the centuries. This type of changing space may benefit from this type of map tagging, but a space that changes from time to time is more difficult to visualise and understand; it benefits more from this approach. Anything cyclic is continuously occilating and so at the same time it contains more than one space, something which the aforementioned Smithfield Park example did not. Daily, weekly, seasonal: all of these things are mentioned in Gay's poem and could be understood in a new way by "tagging" the labels. An example of the cyclic tag is what Jess mentioned: the Winter section of the poem shows the Thames as a frozen road, before it thaws. There is one tag for winter, one for summer; it could be seen as a seasonal space-change. Temporal mapping becomes an important part of digital cartography.
Food for thought: how do we differentiate the tags? Only visually (as I have done, i.e. different coloured text). Do we have different notes to provide different information? Is it only useful if we have a London full of these tags and, at a glance, can understand different spaces among the same places on a large scale? Does it become statistical (i.e. quantitative rather than qualitative)?