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map-make

A script and code registry to create simple maps using OpenLayers with no need to know or code Javascript: simply specify options in a form or define the same in a json object or custom element.

Objective

Simplify map creation for those with little or no knowledge of Javascript or cartography. Also helps developers try out different options.

Current features

  • raster source definitions stored in a registry (lib/registry/sources); pretty much any raster source supported by OL can be added to this
  • GeoJSON, KML and GPX vector sources can be loaded and displayed over the raster source
  • by default, maps with vector data will initially be zoomed to the extent of the data; those without will be zoomed to the maximum extent of the projection; this can be overridden by specifying a center and zoom level
  • raster sources can be in different projections, and can be made in/visible by the layerswitcher provided by default
  • the layerswitcher will automatically reproject vector features when the projection of the underlying raster source changes (OL's raster reprojection is not used; the view is simply redisplayed using the nearest zoom level for the new projection)
  • uses the default OL zoom and scaleline controls, to which other widgets such as cursor position display, tooltips and feature info popups can be added; these widgets are also stored in a registry (lib/registry/components)
  • custom feature styles can be specified for each vector source
  • vector data/features can be drawn and moved/edited; this includes splitting and joining of linestrings
  • map div uses 100% of screen viewport so keyboard arrows can pan map
  • should be usable on both mouse/keyboard (desktop/laptop) and touch-screen (mobile) devices

Usage

The main html file map-make.html is all that needs to be installed. When loaded in the browser, this will display the main toolbar which enables you to define which sources and tools you wish to use.

This is fine for one-off maps, but is unwieldy for maps you want to reuse, so the map definition (mapDef) can be saved for future use.

This can be a JSON object stored in a file which can be loaded from a url. It can also be a <map-def> custom element defined in the HTML file.

In addition, parameters can be specified as key-value pairs in the query string.

There are some sample mapDefs and sample HTML files to load them in samples/. See Usage file for more detailed instructions and further examples.

Technical details

The JS source is in lib/ and is modularised in ES2015 module syntax (import/export). It runs entirely in the browser, using the jsDelivr CDN to load the appropriate modules direct from this Github repo. The initial entry point is from the HTML file with other modules loaded dynamically from code using import().

For more info on registry entries, see the Readme in the appropriate section of lib/registry.

Until version 3.1, the OL code was compiled into a separate build imported by the map-make modules, but since 3.1 the OL and map-make code has been built together, split into modules for each of the different entry points.

map-make.html loads initloader.js as the initial bootstrap, by default from dist on Github master, served from jsDelivr. This is a standard script, not a module. A field in initloader defines the latest version, and by default, it loads CSS from dist/css/ for this version, and modules from dist for this version, using initloader's URL as the base URL. This can however be overridden to enable loading a different version or from localhost. A test HTML could, for example, load a local initloader, and both CSS and base URL can be defined in a data-configVars attribute in the <script> tag:

<script data-configVars='{"css":"../another/path/css/map-make.css","baseURL":"./further/path/map-make/lib/"}' src="../map-make/lib/initloader.js"></script>

A new version can thus be pushed to Github, and tested there; only when the release tag is added, and the tag field is changed in initloader, will this be used by default. See below for more on the release procedure, and initloader.js source for more info.

External libraries

Besides OL, a modular build of Proj4js is used by the projection modules (registry/projections), slideout.js by the toolbar component, and Awesomplete by the addlayer component for autocompletion. Until these libraries produce ES-module versions, the last two are wrapped in an export default so they can be imported. See lib/registry/projections/Readme.md for details of the Proj4js custom build. The CSS for OL, Font Awesome and Slideout is combined into one file (css/map-make.css), which is minified into dist/css/; that for Awesomplete is loaded from CDN from the addlayer component. A custom version of the Font Awesome webfont including only those glyphs used is loaded by map-make.css.

More on lib and dist

As discussed above, the source is in lib, with a built/minified version in dist. The source imports OL modules using ol/... specifiers. An import map can then determine where ol/ should be loaded from - for example, from localhost or from the repo. The build process takes these modules, also using an import map to load the OL code from the repo, and builds each of the entry modules into dist.

So, lib/ contains:

  • uncompressed module sources which can be loaded for testing on localhost
  • compressed code for external libraries in registry/components/ext/; these are in a simple export default wrapper so they can be loaded as dependencies
  • component HTML in registry/components/*.html.js are <template> elements in a simple export default wrapper so they can be loaded as dependencies

dist/ is built from lib using deno-rollup, a port of Rollup for Deno, with drollup.split.js as the config file. This is run with deno run -A --unstable ./drollup.split.js, which combines the map-make and OL code, and splits into modules corresponding to the dynamically imported map-make modules. This uses an import map to define where the external source is loaded from; see build page for more details. The modules are minified using deno-rollup's Terser plugin, and using the module option so top-level names can be mangled.

The component ext/ files are included in the build, but the proj4js files are at the moment kept external.

dist/ also contains css and font directories.

Raster sources

Some source providers require an API code to be given when fetching tiles; these are specified in the appropriate source files, and should be provided at runtime in the map definition.

Limitations

Only 1 raster layer can be active/visible at a time.

At present, there is no error validation at all.

Because this software is based on new language features like modules, it will not work in old browsers such as IE.

Future plans

See issues.

Contributions

are welcome, as are all good ideas on how this can be developed further.

Release process

Code is loaded from a release tag. As mentioned above, which release tag to use is defined in initloader.js. So:

  • changes can be committed and pushed to Github without affecting the loaded code
  • for new release, add a new tag (git tag n.n.n) and git push --tags
  • change initloader.js to use new tag/release; when pushed to Github, this release will be used once jsDelivr's cache has cleared.

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