98 lines
3.8 KiB
Markdown
98 lines
3.8 KiB
Markdown
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# @turf/center-median
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<!-- Generated by documentation.js. Update this documentation by updating the source code. -->
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## centerMedian
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Takes a [FeatureCollection][1] of points and calculates the median center,
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algorithimically. The median center is understood as the point that is
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requires the least total travel from all other points.
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Turfjs has four different functions for calculating the center of a set of
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data. Each is useful depending on circumstance.
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`@turf/center` finds the simple center of a dataset, by finding the
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midpoint between the extents of the data. That is, it divides in half the
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farthest east and farthest west point as well as the farthest north and
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farthest south.
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`@turf/center-of-mass` imagines that the dataset is a sheet of paper.
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The center of mass is where the sheet would balance on a fingertip.
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`@turf/center-mean` takes the averages of all the coordinates and
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produces a value that respects that. Unlike `@turf/center`, it is
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sensitive to clusters and outliers. It lands in the statistical middle of a
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dataset, not the geographical. It can also be weighted, meaning certain
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points are more important than others.
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`@turf/center-median` takes the mean center and tries to find, iteratively,
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a new point that requires the least amount of travel from all the points in
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the dataset. It is not as sensitive to outliers as `@turf/center-mean`, but it is
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attracted to clustered data. It, too, can be weighted.
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**Bibliography**
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Harold W. Kuhn and Robert E. Kuenne, “An Efficient Algorithm for the
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Numerical Solution of the Generalized Weber Problem in Spatial
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Economics,” *Journal of Regional Science* 4, no. 2 (1962): 21–33,
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doi:{@link [https://doi.org/10.1111/j.1467-9787.1962.tb00902.x}][2].
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James E. Burt, Gerald M. Barber, and David L. Rigby, *Elementary
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Statistics for Geographers*, 3rd ed., New York: The Guilford
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Press, 2009, 150–151.
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### Parameters
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* `features` **[FeatureCollection][1]\<any>** Any GeoJSON Feature Collection
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* `options` **[Object][3]** Optional parameters (optional, default `{}`)
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* `options.weight` **[string][4]?** the property name used to weight the center
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* `options.tolerance` **[number][5]** the difference in distance between candidate medians at which point the algorighim stops iterating. (optional, default `0.001`)
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* `options.counter` **[number][5]** how many attempts to find the median, should the tolerance be insufficient. (optional, default `10`)
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### Examples
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```javascript
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var points = turf.points([[0, 0], [1, 0], [0, 1], [5, 8]]);
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var medianCenter = turf.centerMedian(points);
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//addToMap
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var addToMap = [points, medianCenter]
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```
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Returns **[Feature][6]<[Point][7]>** The median center of the collection
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[1]: https://tools.ietf.org/html/rfc7946#section-3.3
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[2]: https://doi.org/10.1111/j.1467-9787.1962.tb00902.x}
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[3]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object
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[4]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String
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[5]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number
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[6]: https://tools.ietf.org/html/rfc7946#section-3.2
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[7]: https://tools.ietf.org/html/rfc7946#section-3.1.2
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<!-- This file is automatically generated. Please don't edit it directly. If you find an error, edit the source file of the module in question (likely index.js or index.ts), and re-run "yarn docs" from the root of the turf project. -->
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---
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This module is part of the [Turfjs project](https://turfjs.org/), an open source module collection dedicated to geographic algorithms. It is maintained in the [Turfjs/turf](https://github.com/Turfjs/turf) repository, where you can create PRs and issues.
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### Installation
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Install this single module individually:
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```sh
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$ npm install @turf/center-median
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```
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Or install the all-encompassing @turf/turf module that includes all modules as functions:
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```sh
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$ npm install @turf/turf
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```
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