The initial form could be built from cheap and easily accessible materials, using foam board initially, covered in paper mache and assorted other materials to provide texture and represent features in the landscape. Reaching all the surface could prove to be an issue, especially in the centre, but as long as you could access it from all sides this should be achievable. At 1.2m square this should be achievable in a small workshop, so space to construct it shouldn’t be an issue.
This initial form would need to be sealed and moulded in rubber and fibreglass to then be modelled in wax. The surface would need to be split up into sections to do this as such a large sheet could not be cast in one section. The wax would then be shelled up and cast, then welded back together into one sheet. The foundry would complete this process though, from the modelling to the finished piece.
The corners would need to be rounded to some extent to prevent injury to passers-by. Being constructed out of bronze it will be durable from the weather and any potential vandalism. Because of the shape of the map tile, the flow of water falling on the sculpture would have to be taken into account. If it was placed horizontal, water would probably pool in the centre of the sculpture and build up gung. Due to this it might be best to introduce a tilt on the tile, possibly quite a big one to make it look deliberate and not just badly lined up.
The size of the piece and the base construction could be modified according to the budget available. Also, as this is planned as the starting point of a sculpture trail around the town, the size and location of the other map tiles would also have to be worked out and budgeted for at the same time.
When constructed, this piece would be very heavy, so would require a truck with a crane to move the piece to site and onto its base. If the base was bronze also, the piece would be moved as a completed piece from the foundry to the site. If the base was concrete (more economical), then it would make sense to produce a cast block of concrete that the top could be bolted to. This could be assembled on site, but it would probably make sense to do this in a safer environment (as you would need to get underneath the concrete block), bolt the two together, then transport the whole piece to site.
Due to the weight of this piece I think it could just sit on top of the paving at the site with perhaps some mortar around the base.
If this was the starting point of a sculpture trail, a notice board describing the route around the sculptures would need to accompany this sculpture.
The curved metal pieces would need to be formed at a plate rolling company at the right curvature, they would probably also be cut to size at the same time. Forming the joining strips of metal would be more of an issue, I imagine the best way of doing this would be to hot or cold work the metal to introduce the curves? This might have to be constructed out of thinner steel to allow this to be done and perhaps have two pieces together to provide the strength required. Because of the size of this sculpture, workshop space would probably need to be hired to have enough space to create it.
I don’t think there is much scope for budget creep with these sculptures (unless you reduced the number of sections), so the costs of providing the curved metal sections would need to be fixed before agreeing the budget.
It would need to be constructed from weather resistant core-10 steel to ensure that it keeps its integrity as time goes on, as normal steel would continue to rust and eventually become unstable.
When constructed, this piece would also be very heavy, so would require a truck with a crane to move the piece to site and onto its base. It could be constructed to its full height and moved as one piece, or it could be moved in sections and welded together on site.
To fix this in place it would probably be best to weld it to a number of reinforcing steel bars which could then be set into concrete. A deep hole would need to be dug on site for this concrete base. A surveyor/architect would need to be employed to calculate the concrete pad and correct dimensions of steel bar to which would be required to do this correctly and safely.
It would probably be best to construct the piece in two sections, the bottom piece a single section with the reinforcing steel bars which could be set into a concrete base and left to set. The top section could then be welded on top at a later date.
One danger that would need to be accounted for would be the potential for this sculpture to be used as a climbing frame by the public. The initial idea of bolts holding it together might not be a good idea because of the hand/footholds they would offer, so rounded rivet-like shapes may be a better option.