Comments for Volunteered Geographic Information

Comment on ArcGIS 10 – Field Calculator and Python by Troels Petersen

Troels Petersen — Wed, 25 Jan 2012 16:40:02 +0000

Thanks a lot! I wasn’t able to find any helpful information about python and the field calulator on the ESRI pages.

Comment on Generalising OS MasterMap Buildings by Daniel Lewis

Daniel Lewis — Wed, 04 Jan 2012 18:01:22 +0000

The enclosing rectangles are orientated so that they have the smallest possible area in completely covering each individual building polygon – this means that the rectangle should account for buildings which are not north-south or east-west in orientation, as it rotates the rectangle for best fit. The merge here is a little rudimentary, I apply a small buffering operation – enough to fill any small gaps between houses, but not enough to cross a road (really a matter of a metre or two) and then dissolve, or merge, the polygons that subsequently overlap. As many of the houses in the area are terraced, the complexity of long buildings with many subdivisions is simplified. As noted, there are sophisticated algorithms to do this – orthogonal simplification – but I didn’t really have access to them, since this slightly cobbled together procedure!

Comment on Generalising OS MasterMap Buildings by Michal Migurski

Michal Migurski — Thu, 22 Dec 2011 16:27:24 +0000

Can you say more about the enclosing rectangles? Are they oriented north-south, or with respect to the building? How do you decide which polygons to merge together? Looks great!

Comment on Apple’s iPad and Mobile/Field GIS by Joe Wilson

Joe Wilson — Mon, 05 Dec 2011 18:53:47 +0000

Our suite of GIS iPad/iPhone apps speak for themselves.

GIS Pro: http://itunes.apple.com/us/app/gis-pro/id459109672?mt=8

GIS Kit: http://itunes.apple.com/us/app/gis-kit/id429688355?mt=8

Comment on Jenks’ Natural Breaks Algorithm in Python by Doug Curl

Doug Curl — Mon, 14 Nov 2011 23:31:39 +0000

This is really great. I was able to adapt your Python code for Javascript to make ArcGIS Server Javascript API chloropleth maps on-the-fly…I think successfully. The code is published here and, hope you don’t mind, but I also cited this page and your code: http://www.arcgis.com/home/item.html?id=0b633ff2f40d412995b8be377211c47b

Comment on A Thematic Map in Python by More news from the shed… | SomeBeans

More news from the shed… | SomeBeans — Sun, 02 Oct 2011 07:49:13 +0000

[...] for a library to display the resulting maps but after a brief search I adapted the simple methods here for drawing maps using [...]

Comment on A Spatial Approach to Location Quotients by Spencer

Spencer — Wed, 14 Sep 2011 05:35:03 +0000

Also worth checking out: http://ideas.repec.org/p/por/fepwps/273.html
Describes a fairly simple significance test for the location quotient, I used it for the maps in:
http://www.tfl.gov.uk/microsites/freight/documents/GLAEconomicswp37.pdf

Comment on Apple’s iPad and Mobile/Field GIS by CMTINC

CMTINC — Fri, 02 Sep 2011 19:32:36 +0000

Hi Daniel,

Have you looked at the iCMTGIS for iPAD that was released earlier this year? Please download this free professional GIS application from the iTunes Store and let us know how you like it. Thanks.

Comment on Weighted Mean Direction Surfaces in Python by Martin Zaltz Austwick

Martin Zaltz Austwick — Wed, 31 Aug 2011 13:56:34 +0000

You can also brute force it fairly easily; take a weight sum of the signs and cosines and then compute the arctan of the resulting ratio, so:

Theta = arctan( [sum_i w_i sin(theta_i)] / [sum_i w_i cos(theta_i)])

where w_i are the weights and theta_i in the angles of each element. This is essentially what the complex numbers approach is doing, albeit less explicitly.

Comment on More Thematic Maps in Python – shapely and descartes by Daniel Lewis

Daniel Lewis — Wed, 31 Aug 2011 12:12:19 +0000

I’ve not had an opportunity to look at mapscript I’m afraid, looks interesting though, thanks for flagging it.