geogrid.js

The library geogrid.js provides a Leaflet layer that depicts data aggregated by the ISEA3H Discrete Global Grid System. Thereby, the library renders the visualization using WebGL.

Scientific Publications

The following publication is related to this plugin and the used Discrete Global Grid System (DGGS):

F-B Mocnik: A Novel Identifier Scheme for the ISEA Aperture 3 Hexagon Discrete Global Grid System. Cartography and Geographic Information Science 46(3), 2019, 227–291

Related Software

This library is compatible with the framework Measures REST, which can be used to aggregate data by a grid and then provide the data via a REST interface. Data can also be aggregated manually by using the library geogrid that computes and handles Discrete Global Grid Systems (DGGS).

Use the Library

To load the library, include the following in the header of your HTML file:

<script src="https://unpkg.com/geogrid.js"></script>

In addition, the library geogrid.js requires the following libraries to be loaded:

The library vptree.js library is included and shipped with geogrid.js under the ISC license.

In order to use the ISEA3HLayer, a Leaflet map needs to be loaded first, for example, like follows:

var map = L.map('map').setView([49.4, 8.7], 10);

Then, the ISEA3HLayer, which is provided by this library, can be added:

var isea3h = L.isea3hLayer({
  url: 'http://localhost:8080/.../{z}/{x}/{y}.json',
}).addTo(map);

As an option, a URL needs to be provided under which data aggregated by the ISEA3H grid is available. Such a URL can be provided in two different formats:

in an XYZ tile format by including the paramters {x}, {y}, and {z}, thus allowing to load the data on demand, and
as a API URI that provides the data corresponding for a given bounding box {bbox} and resolution {resolution}.

In both cases, further parameters can be encoded, as is discussed in the description of the option parameters. In all cases, the provided data should be formatted as follows:

{
    "type":"grid",
    "resolution":14,
    ...
    "data":[
        {"value":0.345, "id":"1309502766029885663"},
        {"value":null, "id":"1309502851015240491"},
        ...
    ]
}

The grid cell IDs are assumed to conform to both adaptive and non-adaptive IDs, as is described in:

F.-B. Mocnik: A Novel Identifier Scheme for the ISEA Aperture 3 Hexagon Discrete Global Grid System. Cartography and Geographic Information science 46(3), 2019, 277–291. doi:10.1080/15230406.2018.1455157

Data which is formatted in the above format is, for example, provided by the framework Measures REST.

The ISEA3HLayer can be used in combination with different base maps. A good choice is Toner lite by Stamen. The complete code of the example is as follows:

var map = L.map('map').setView([49.4, 8.7], 10);
L.stamenTileLayer('toner-lite').addTo(map);
L.isea3hLayer({
  url: 'http://localhost:8080/.../{z}/{x}/{y}.json',
}).addTo(map);

Examples

An example can be found in the subdirectory example. Observe that the example index-with-server.html presumes a local instance of Measures REST.

Examples: Options

The ISEA3HLayer accepts several options, which allow to easily adapt the layer to the data source and the visualization needs. Instead of depicting representing the value related to a grid cell by the colour, the value can also be encoded by the size of the grid cell:

L.isea3hLayer({
  url: '...',
  cellColorKey: null,
  cellSizeKey: 'value',
})

Even two different values related to a grid cell can be represented, for example, the value with key value1 encoded by the colour, and the value with key value2, by the size of the cell:

L.isea3hLayer({
  url: '...',
  cellColorKey: 'value1',
  cellSizeKey: 'value2',
})

Most options can even be updated after the ISEA3HLayer has been initialized, which makes possible to interactively adapt the display and depict different aspects of the data without the need to reload them:

isea3h = L.isea3hLayer({
  url: '...',
  cellColorKey: 'value1',
})
...
isea3h.update({
  cellColorKey: 'value2',
})

Examples: Several Data Sources

The ISEA3HLayer accepts one or more data sources. In many cases, only one data source is to be depicted. This is the case that has been discussed before – the URL that provides reference to the data and other options are provided as options:

L.isea3hLayer({
  url: '...',
  cellColorKey: 'value1',
  cellSizeKey: 'value',
  silent: false,
  renderer: 'webgl',
})

Observe that the options silent and renderer do not refer to this particular dataset but the layer in general. This is in contrast to the options url, cellColorKey, and cellSizeKey, which refer to the data source and its representation. Instead of mixing these options (which is allowed), they can be separated as follows:

L.isea3hLayer({
  sources: [{
    url: '...',
    cellColorKey: 'value1',
    cellSizeKey: 'value2',
  }],
  silent: false,
  renderer: 'webgl',
})

This way of providing the options has the advantage that it becomes obvious which options are only valid for the provided data source, and it allows to add additional data sources. For instance, several sources can be provided as follows:

L.isea3hLayer({
  sources: [{
    url: '...',
    cellColorKey: 'value1',
    cellSizeKey: 'value2',
  }, {
    url: '...',
    cellColorKey: null,
    cellSizeKey: 'value',
  }],
  silent: false,
  renderer: 'webgl',
})

It is important to note that the two ways of noting down the sources – inline with the general options in case of one source, or under sources in case of one or more sources – cannot be mixed.

The several options available are described in the following.

Options

The following options are available to describe the data sources and their handling:

Option	Type	Default	Description
`url`	`String`	`null`	URL under which data aggregated by the ISEA3H grid is available. The URL potentially contains information about the bounding box and the resolution, encoded by `{bbox}` and `{resolution}` respectively. Further parameters can be used in the `url` by providing corresponding values in the option `parameters`. The expected format of the returned data is described above.
`data`	`Object`	`null`	Instead of the parameter `url`, the data can be provided explicitly.
`parameters`	`Object`	`{date: new Date().toLocaleDateString(), dateFrom: null}`	Additional parameters that can be used in the `url`.
`hide`	`Boolean`	`false`	Determines whether the source should be hidden. Can be useful for empty grids that are used to make incomplete data complete.
`tileZoom`	`Number`	`7`	Zoom to be used for the tiles in case of a tile URL.
`cellColorKey`	`String`	`value`	The colour to be used for a grid cell can be chosen in dependence of the property `cellColorKey` of the cell. The colour is, accordingly, determined by computing the function `cellColorScale` with the property `cellColorKey` of the cell as argument. If the option `cellColorKey` is `null`, the colour `cellColorNoKey` is used instead.
`cellColorMin`	`Number`	`0`	Minimum value to be used in `cellColorScale`. If `null`, the minimum value is determined by the data of the currently cached cells.
`cellColorMax`	`Number`	`null`	Maximum value to be used in `cellColorScale`. If `null`, the maximum value is determined by the data of the currently cached cells.
`cellColorScale`	`Function`	`(min, max) => d3.scaleLinear().domain([min, max]).range(['#fff', '#f00'])`	This option is used to determine the colour to be used for a grid cell, when `cellColorKey` is not `null`. This option is either (1) a function that returns, for a the property `cellColorKey` of the cell, the colour that should be used for the cell; or (2) a function that returns for given `min` and `max` values a function as in (1).
`cellColorNoData`	`String`	`'#eee'`	Colour to be used for a grid cell, when no data is available for this particular cell.
`cellColorNoKey`	`String`	`'#f00'`	Colour to be used for a grid cell, when `cellColorKey` is `null`.
`cellColorOpacity`	`Number`	`.5`	Opacity of the area of the grid cells.
`cellSizeKey`	`String`	`null`	The relative size of a grid cell can be chosen in dependence of the property `cellSizeKey` of the cell. The relative size is, accordingly, determined by computing the function `cellSizeScale` with the property `cellSizeKey` of the cell as argument. If the option `cellSizeKey` is `null`, the relative size `cellSizeNoKey` is used instead.
`cellSizeMin`	`Number`	`0`	Minimum value to be used in `cellSizeScale`. If `null`, the minimum value is determined by the data of the currently cached cells.
`cellSizeMax`	`Number`	`null`	Maximum value to be used in `cellSizeScale`. If `null`, the maximum value is determined by the data of the currently cached cells.
`cellSizeScale`	`Function`	`(min, max) => {return value => (value - min) / (max - min)}`	This option is used to determine the relative size to be used for a grid cell, when `cellSizeKey` is not `null`. This option is either (1) a function that returns, for a the property `cellSizeKey` of the cell, the relative size that should be used for the grid cell; or (2) a function that returns for given `min` and `max` values a function as in (1).
`cellSizeNoData`	`Number`	`0`	Relative size to be used for a grid cell, when no data is available for this particular cell.
`cellSizeNoKey`	`Number`	`1`	Relative size to be used for a grid cell, when `cellSizeKey` is `null`.
`dataKeys`	`Array`	`...`	List of data keys to be copied for each cell. By default, this list is determined automatically, which presumes that all keys are present for the first cell provided.
`dataMap`	`Function`	`d => d`	Determines the data used for the corresponding cell, based on the list item provided in the json data. This can, e.g., be used for more complex scenarios where timeline data is provided for each cell.
`dataTransform`	`Function`	`data => data`	Is used to transform the entire dataset provided or downloaded, e.g., for aggregating data into cells. In contrast to `dataMap`, which only affects the data of one cell, `dataTransform` affects the entire dataset.

In addition, the following general options are available:

Option	Type	Default	Description
`sources`	`List`	`null`	List of data sources, each of them exposing the options listed above.
`silent`	`Boolean`	`true`	Enables silent mode. When enabled, debug information is suppressed in the console.
`debug`	`Boolean`	`false`	Enables debug mode. When enabled, the grid cells are highlighted, and debug information is shown in the console (`silent` is `false`).
`cellContourColor`	`String`	`'#fff'`	Colour to be used for the contour of a cell.
`cellContourWidth`	`Number`	`2`	Width of the contour of a cell.
`cellContourOpacity`	`Number`	`1`	Opacity of the contour of a cell.
`cellCentroidColor`	`String`	`null`	Color of the dot representing the centroid of a cell.
`cellCentroidRadius`	`Number`	`1`	Radius of the dot representing the centroid of a cell.
`cellCentroidOpacity`	`Number`	`1`	Opacity of the centroid of a cell.
`colorProgressBar`	`String`	`'#ff5151'`	Colour of the progress bar shown when loading new data.
`colorDebug`	`String`	`'#1e90ff'`	Colour used to highlight certain aspects when using the `debug` mode.
`colorDebugEmphasized`	`String`	`'#f00'`	Colour used to highlight very important aspects when using the `debug` mode.
`resolution`	`Function`	`...`	A function which results, for a given zoom level of the map as input parameter, a resolution of the grid
`attribution`	`String`	`'plugin © <a href="http://www.geog.uni-heidelberg.de/gis">Heidelberg University</a> and <a href="http://www.mocnik-science.net">Franz-Benjamin Mocnik</a>'`	Attribution to be shown.
`bboxViewPad`	`Number`	`1.05`	Size of the bounding box for which data is rendered in the layer, when the view of the map has changed (moving the view, changing the zoom level, etc.)
`bboxDataPad`	`Number`	`1.25`	Size of the bounding box for which data is requested using the `url`, when the view of the map has changed (moving the view, changing the zoom level, etc.)
`renderer`	`'webgl'`\|`'svg'`	`'webgl'`	Renderer to be used. The WebGL renderer (default choice) is much faster than the SVG renderer, but the SVG renderer might offer advantages in some scenarios where a interaction is crucial.
`pureBBox`	`L.LatLngBounds`	`null`	Bounding box for which the data is downloaded in case of the pure function (`L.isea3hToGeoJSON`; see below).
`pureResolution`	`Number`	`7`	Resolution that is used for the data download in case of the pure function (`L.isea3hToGeoJSON`; see below).

Methods

The ISEA3HLayer has the following methods to add or remove it to/from a Leaflet map object, and to update its options:

Method	Description
`addTo(map)`	Adds the layer to the given `map`.
`removeFrom(map)`	Removes the layer from the given `map`. The layer is destroyed and cannot be re-used.
`hideFrom(map)`	Hides the layer from the given `map`. When needed, the layer can be added to the same or another map at a later point in time.
`update(options)`	Updates the options of the layer. The layer is rendered or even re-computed if necessary.
`updateSources(sources)`	Updates the list of sources, including the source-specific options.

Events

The following events are available:

Event	Description
`dataDownloaded`	This event is fired whenever new data is downloaded.
`loadComplete`	This event is fired when the data has been rendered the first time.

Plugins

The functionality of the ISEA3HLayer can be extended by plugins. Such plugins can easily be added to the layer:

var isea3h = L.isea3hLayer({...});
isea3h.addPlugin(L.testPlugin());

The following plugins are available:

more plugins are to be implemented

Authoring Plugins

General Structure of a Plugin

Plugins extend the class L.ISEA3HLayerPlugin. Several methods exist that can be overwritten in order to react to certain events. A plugin can, for example, be implemented as follows:

class TestPlugin extends L.ISEA3HLayerPlugin {
  onHover(e) {
    console.debug('hover', e.cell.id, e.data.value)
  }
  onUnhover(e) {
    console.debug('unhover', e.cell.id, e.data.value)
  }
  onClick(e) {
    console.debug('click', e.cell.id, e.data.value)
  }
  ...
}

In addition to a class, a factory method should be provided in order to simplify the instantiation of the plugin:

L.testPlugin = () => new TestPlugin()

Events

Plugins to the ISEA3HLayer follow the paradigm of reactive programming: changes in the system that consists of the map and the user fire events of the plugin. The corresponding method to an event is only executed, in case it is implemented. The method onHover is, for example, executed when the hover event is fired. If a corresponding method is not present, no error is thrown. The following event listeners can be used:

Event listener	Description
`onHover`	the cursor hovers a cell
`onUnhover`	the cursor moves out of a cell
`onClick`	the user clicks on a cell

Methods

Plugins can react to events by performing an action as soon as an event is triggered. Such an action can change the state of the ISEA3HLayer, or other parts of the website. As an example, a cell can be drawn in blue colour when it is hovered by the courser:

onHover(e) {
  this.setCellColor(e.cell, 'blue')
  this.render()
}

The URL that is used to retrieve data from a server contains parameters. Among these parameters are the resolution and the bounding box, but potentially also additional parameters. These additional parameters can, for example, be set as follows:

this.setParameter('date', '2017-01-01')
this.downloadData()

Some of the functions except a callback as parameter because the result is computed asynchronously:

onHover(e) {
  this.neighbors(e.cell, cells => {
    console.debug(cells)
  })
}

The following methods of the L.ISEA3HLayerPlugin are available:

Method	Description
`downloadData()`	Forces the data to be downloaded anew. After having downloaded the data, the method `render` is automatically executed.
`render()`	Forces the layer to render.
`neighbors(cell, callback)`	Computes the direct neighbours of the grid cell `cell`. The function `callback` is called with the list of neighbouring cells as an argument.
`getParameter(parameter)`	Gets the value of a parameter. Such parameters can be used in the URL when requesting data from the server.
`setParameter(parameter, value)`	Sets a parameter. Such parameters can be used in the URL when requesting data from the server. The method `downloadData` needs to be called to make the change effective.
`setCellColor(cell, color)`	Sets the colour of the grid cell `cell` to `color`. If `color` is `null`, the colour of the grid cell is computed by using the options `cellColor*`. The method `render` needs to be called to make the change effective.
`resetCellColor()`	Resets the colours set by `setCellColor`. The colour of all grid cells are thus computed by using the options `cellColor*`. The method `render` needs to be called to make the change effective.
`setCellSize(cell, size)`	Sets the relative size of the grid cell `cell` to `size`. If `size` is `null`, the relative size of the grid cell is computed by using the options `cellSize*`. The method `render` needs to be called to make the change effective.
`resetCellSize()`	Resets the sizes set by `setCellSize`. The relative size of all grid cells are thus computed by using the options `cellSize*`. The method `render` needs to be called to make the change effective.
`setCellContourColor(cell, color)`	Sets the contour colour of the grid cell `cell` to `color`. If `color` is `null`, the contour colour of the grid cell equals the option `cellContourColor`. The method `render` needs to be called to make the change effective.
`resetCellContourColor()`	Resets the contour colors set by `setCellContourColor`. The contour color of all grid cells thus equals the option `cellContourColor`. The method `render` needs to be called to make the change effective.
`setCellContourWidth(cell, width)`	Sets the contour width of the grid cell `cell` to `width`. If `width` is `null`, the contour size of the grid cell equals the option `cellContourWidth`. The method `render` needs to be called to make the change effective.
`resetCellContourWidth()`	Resets the contour widths set by `setCellContourWidth`. The contour width of all grid cells thus equals the option `cellContourWidth`. The method `render` needs to be called to make the change effective.

Compute GeoJSON only

In some cases, one might not want to visualize grid data by the use of Leaflet but to only compute the corresponding GeoJSON. The library thus provides a corresponding function to compute the GeoJSON in an efficient way. For this, neither of the libraries needs to be loaded. For data formatted as described at the top of this page, the GeoJSON can be computed as follows:

L.isea3hToGeoJSON({
  data: data,
}, geoJSON => console.log(geoJSON))

Instead of the data, a url can be provided as well. In this case, the bounding box and the resolution can be provided.

L.isea3hToGeoJSON({
  url: '...',
  pureBBox: null,
  pureResolution: 7,
}, geoJSON => console.log(geoJSON))

Note that the result is communicated by a callback, and that many options have no effect in this case.

Build geogrid.min.js

The library can be translated from ECMAScript 6 to minified JavaScript, which results in a file geogrid.min.js. In order to generate this minified file, you have to install Node.js first. Thereafter, you have to execute the following command:

npm install

This command automatically also builds the library. Whenever you want to re-build the thereafter, just run:

npm run build

The resulting minified file can be found in the subdirectory dist, which is created during this process. In addition, a JavaScript Source Map is created.

Known Bugs

The following bugs are known but not yet addressed:

Downloaded data cached for the n-th source is not removed from the cache when updating the list of sources to have less than n sources.
Missing tiles are not handled correctly.

Author

This software is written and maintained by Franz-Benjamin Mocnik, [email protected].

In 2017–2019, this software has been supported by the DFG project A framework for measuring the fitness for purpose of OpenStreetMap data based on intrinsic quality indicators (FA 1189/3-1).

All commits after 9/2019 (c) by Franz-Benjamin Mocnik, 2019–2020. All commits before 8/2019 (c) by Heidelberg University, 2017–2019.

License

The code is licensed under the MIT license.

Name		Name	Last commit message	Last commit date
Latest commit History 200 Commits
.github		.github
docs/images		docs/images
example		example
src		src
.babelrc		.babelrc
.gitignore		.gitignore
LICENSE		LICENSE
README.md		README.md
developer-guidelines.md		developer-guidelines.md
package.json		package.json
webpack.config.js		webpack.config.js

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geogrid.js

Scientific Publications

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Use the Library

Examples

Examples: Options

Examples: Several Data Sources

Options

Methods

Events

Plugins

Authoring Plugins

General Structure of a Plugin

Events

Methods

Compute GeoJSON only

Build geogrid.min.js

Known Bugs

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geogrid.js

Scientific Publications

Related Software

Use the Library

Examples

Examples: Options

Examples: Several Data Sources

Options

Methods

Events

Plugins

Authoring Plugins

General Structure of a Plugin

Events

Methods

Compute GeoJSON only

Build geogrid.min.js

Known Bugs

Author

License

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