Moore Spatial

GIS and Related Pursuits

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Upsidedown Maps With OpenLayers3!

Openlayers3 lets you rotate the 2d viewport. This functionality can be used to make upsidedown maps, so I did.

Code on GitHub
Demo on GitHub.io

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Adding To the Leaf Pile

I recently presented at the 2013 MN GIS/LIS conference on leaflet plugin development. You can now see my demo and presentation online.

I demonstrate three ways to write leaflet plugins.

  1. Adding a new method to an existing Leaflet object
  2. Overriding an existing method in an existing Leaflet object
  3. Extending an existing Leaflet object to create your own object

 

The presentation can be found here:

PDF, Google Docs PDF, SlideShare

 

The Demo can be found here:

Leaflet-Spiders Demo on MooreSpatial.com

Leaflet-Spiders Demo on GitHub

 

The code can be found here:

GitHub

 

Happy Hacking!

 

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What Slippy Map Zoom Level Is Ideal For My Source Map?

If you’re creating XYZ tiles for your slippy map (eg. Leaflet or OpenLayers), and your source is a raster image, you might wonder which zoom level will display the map with the least artifacts.

Or you might not. In any case, if you do want to know what zoom level is ideal, here’s how you find it. The code is in PHP, but should be easy to translate to other languages.

$min_dimension = min($image_width_in_pixels,$image_height_in_pixels);
$zoom_level = round(log($min_dimension/256,2)

Take the smaller of the height or width[1], divide it by 256 and find the base-2 logarithm of that. You will likely need to round that result to get an integer value. That integer will be the zoom level which has to resize your image the least to produce the appropriate tiles.

[1] Really, your source map should likely be square since you’re probably using Web Mercator

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A Review of Maps.Familysearch.Org

FamilySearch.org is on of the bigger genealogy websites with a large repository of digitized and microfilmed documents, a huge collection of pedigrees, and online pedigree management tool among other things. They also have an ongoing FamilySearch Labs program where they try out new technologies and product concepts. One of their current Labs projects is http://maps.familysearch.org.

Historic Maps of England

Maps.FamilySearch.org

Maps.FamilySearch.org

They currently only have maps of England available and only for 1851. For 1851 you can choose a variety of overlays including the parish, county, poor law union and province boundaries. For some types, such as parish boundaries, you can click a parish and get an info box indicating when records are available for that parish., or click a county and get a list of parishes in that county.

Hope for Future Directions

The current state of http://maps.familysearch.org is a single point in time for a single location. If the project makes it out of labs I hope and expect that they will extend it worldwide and across time. Geocoding the boundaries for their many datasets of genealogical records would be quite a process, but FamilySearch routinely undertakes and is involved in huge digitization projects and does a good job with them.

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A Review of Pastmapper.com

Welcome to my spatiotemporal GIS blog! Here I intend to publish reviews, questions and links to interesting studies, presentations and products dealing with old maps, GIS, GIS and genealogy and anything else tangentially related or interesting.

We’re going to start it off with a short review of Pastmapper.com which describes itself as “a new platform for describing the world of the past“.

Pastmapper presents San Francisco in 1853, 1914 and 2012 and San Mateo in 1853 and 2012. It overlays the old city directory information as points of interest on the map. They have several city directories available for different cities, but it doesn’t look like the other cities have been mapped yet.

One thing I really like about Pastmapper is that they provide a separate base map for 1853 and the present, allowing you to see how far San Francisco has extended into the sea. The points of interest don’t move between the two maps, and there’s no indication of which points are still around and which have disappeared. This is beneficial if you’re trying to find the present-day location of an old establishment, but could be confusing if points of interest were shown from more than one time period, or if more than one time period were available.

Animated Past Mapper screenshot, switching between 1853 and 1812

Animated Past Mapper screenshot, switching between 1853 and 1812

In one of their blog posts Pastmapper says “Online maps today simply add layers of information onto today’s map. Pastmapper is a first step towards answering ‘What was here?’ or ‘Whatever happened to..?’, by delivering a map, not just a data layer, that takes a fourth-dimensional view.“. On this count Pastmapper does a nice job.

Their main page says that they are a “new platform for describing the world of the past” but it’s unclear when Pastmapper will be available for others to use, if at all. What’s on the website is an Alpha release, so it’s possible that we’ll all get to play with it some day with our own data and locations.

Lastly, for anyone who is concerned about the state of the project a tweet from just a few days ago indicates that the project is still alive:

https://twitter.com/pastmapper/status/257555649951563777

My brain is exploding thanks to @andrewxhill‘s talk on @cartoDB at @sotmus. Pastmapper will be getting cooler soon.

 

Hopefully we’ll see some updates we can play with soon!