Map segmentation
# Map segmentation

In mathematics, the map segmentation problem is a kind of optimization problem. It involves a certain geographic region that has to be partitioned into smaller sub-regions in order to achieve a certain goal. Typical optimization objectives include:

* Minimizing the workload of a fleet of vehicles assigned to the sub-regions;
* Balancing the consumption of a resource, as in fair cake-cutting.
* Determining the optimal locations of supply depots;
* Maximizing the surveillance coverage.

Fair division of land has been an important issue since ancient times, e.g. in ancient Greece.

## Notation

There is a geographic region denoted by C ("cake").

A partition of C, denoted by X, is a list of disjoint subregions whose union is C:

    $C=X_{1}\sqcup \cdots \sqcup X_{n}$

There is a certain set of additional parameters (such as: obstacles, fixed points or probability density functions), denoted by P.

There is a real-valued function denoted by G ("goal") on the set of all partitions.

The map segmentation problem is to find:

    $\arg \min _{X}G(X_{1},\dots ,X_{n}\mid P)$

where the minimization is on the set of all partitions of C.

Often, there are geometric shape constraints on the partitions, e.g., it may be required that each part be a convex set or a connected set or at least a measurable set.

## Examples

1. Red-blue partitioning: there is a set $P_{b}$ of blue points and a set $P_{r}$ of red points. Divide the plane into $n$ regions such that each region contains approximately a fraction $1/n$ of the blue points and $1/n$ of the red points. Here:

* The cake C is the entire plane $\mathbb {R} ^{2}$;
* The parameters P are the two sets of points;
* The goal function G is

       $G(X_{1},\dots ,X_{n}):=\max _{i\in \{1,\dots ,n\}}\left(\left|{\frac {|P_{b}\cap X_{i}|-|P_{b}|}{n}}\right|+\left|{\frac {|P_{r}\cap X_{i}|-|P_{r}|}{n}}\right|\right).$
    It equals 0 if each region has exactly a fraction $1/n$ of the points of each color.

## Related problems

* A Voronoi diagram is a specific type of map-segmentation problem.
* Fair cake-cutting, when the cake is two-dimensional, is another specific map-segmentation problem when the cake is two-dimensional, like in the Hill–Beck land division problem.
* The Stone–Tukey theorem is related to a specific map-segmentation problem.
