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Validation

A multiscalar tools set of "simulation outputs mining" :

In order to calibrate the model and to validate it, as well as to valorise the different results of the simulations, two multiscalar tools of "simulation outputs mining" have been developed.

  • The first tool is an interactive. It is dedicated to the calibration phase: it is possible to visualize the state of each parameter or variable, at any time t, of the simulation. A particular care has been put in editing windows for defining the parameters that are a function of time (figure 1). The same tool is used for a rough visualisation of the simulation. During the calibration phase, it allows for instance to follow precisely the values of several attributes of one city step by step, or to explore at a time t the different values of an attribute among a set of cities. (figure 2). Some graphics representing global evolution are also proposed for population, production...in order to control very quickly the order of magnitude of some target variables.

  • The second tool is dedicated to the validation phase, during which the main objectives are:

    • To test the coherence of the rules introduced in the model,

    • To evaluate the ability of the model to reproduce trajectories which are realistic according to what is observed,

    • To get an insight in its sensitivity to initial conditions and parameter variations.

control widget for adjusting a parameter value
A Control Widget for adjusting a parameter value / date

Snapshot of the Simpop2 Eurosim viewer
Snapshot of the Simpop2 Eurosim viewer

 

The potential outputs of the simulations represent a huge amount of data. For instance in Eurosim, the output for one simulation concerns 5000 towns and cities, 100 time steps, 13 functions and all interactions associated to communications and exchanges between the cities. Therefore, the second tool is less interactive. Its output presents a necessary systematic exploration of the simulation results, focusing on three central dimensions :

  • Time

  • Spatial context (in a multiscalar framework)

  • Interactions

The tool offers some systematic procedure of analysis of all the outputs of a simulation. The principle is to "cut-out" the cube of information crossing time, space and functions, using the complementarities of different territorial filters, in order to get a quite complete idea of the different states of the urban system during the successive periods.
Thus, rather than computing a single objective function, in the form of an one-dimensional summary of the simulated values, this tool proposes a multidimensional framework of evaluation of the simulation and integrates a number of measurements on the structures themselves: hierarchical, spatial, functioning...

For each simulation, outputs are summarized and illustrated in a standard report composed of three parts, corresponding to the three geographical levels of interest : Some examples of the variety of outputs are given here.

  • The macro-level concerns the whole space (European urban system for Eurosim or Europe long term), considered at its most aggregate level.

  • The meso-level concerns a series of intermediate results and outputs, corresponding to different kinds of geographical aggregation of the results from the city level. Three kinds of aggregation are considered :

    • Territorial : grouping cities of same region, such as Eastern and Western blocks for Europe, or states

    • Hierarchical : grouping cities of same size category in order to analyse if there exists a systematic size effect in the cities' evolution;

    • Functional : grouping cities with identical specializations, or with the same number of specializations in order to illustrate the effect of different functional levels on differential growth.

  • The local/city level concerns the cities themselves. At this level, the report focuses on the local trajectories associated to population, wealth, labour force, variation rates...and spatial structures of exchange (maps of the market networks, maps of exchanges flows, graphics of evolution of the size of the networks)

The different levels are also analysed through the hierarchical and spatial dimensions of the urban system.

  • The hierarchical structure is illustrated by rank size representations, as well as primacy evolution.

  • The spatial structure is described

    • Either in terms of localisations through global mapping of cities' population and specialization, and its evolution through time.

    • or in terms of interactions through the structure of the exchanges that may be visualized as well as analysed through summaries : evolution of the size.

population at macro-level

growth rate at meso-level

population at city-level

Hierarchical : rank-size graphic

Spatial : location of urban functions

interactions : network of exchanges

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