Wednesday, May 7, 2014

The Joys of Georeferencing

Georeferencing can be a lot of fun.  It can also be a pain.  It, like all GIS processes, requires a lot of patience and problem solving.
But first, what is Georeferencing?  Wikipedia defines it as:  to associate something with locations in physical space.
Simply put it is uploading a aerial photo that was taken being digital data was a thing and referencing points that have stayed the same so the old maps can be accessed digitally.  For instance it would be possible to use Google Earth to look at the City of Austin in 1987.

Sounds easy right?   Not Quite.  There are three major problems with it, development, technology, and margin of error.

Development
How much development could have taken place in the last 20 years?  Surely not enough to make it indistinguishable.

OK.  So a few places are no longer recognizable BUT, there are some landmarks that are sill usable (hence being able to find what those houses used to be).  In another 20 years at Austins current rate of growth however it might indeed be problematic).

Technology
There are problems with both the 1987 method of taking a picture of the region and with ArcMap's algorithm for calculating what goes where.   

In 1987 the US Government would take photos of cities in an attempt to track their development and in case of a natural disaster.  These images were taken by a plane that would snap a photo with a wide focused lens to capture the entire area.  Then these photos would be matched next to each other and a map would be completed.  


This has problems though as the edges of the pictures are not taken straight while digital photography allows us to do the same thing but every point is taken straight.


Digital Technology is not perfect though; if 3 points are georeferenced in a like the "collinear" aspect of the points throws off the algorithm that ArcMap uses and the picture is skewed.  This means that Georeferencers will have to selective choose what points to reference.  


Error
The final problem with Georeferencing is human error.  While it may seem like an electric pole hasn't moved in 20 years it is very possible it has.  Or the shore line of Town Lake, or how some roads have moved 20 or so feet with new construction.  More Over, sometimes I have to leave a large Margin of Error according to ArcMap even though I could reduce it but have a less accurate map.  Georeferencing is sort of an Art.  The more you do it the better you get at it; even if the computer thinks you're wrong.


TIPS
In order to have a good map there are a few little tricks that can help
  1. Fit the map to the display once the displays already looks like the map.  The more accurate you can get it the better.  Some of my maps were georeferenced in 4-5 minutes because it fit nicely and hadnt changed too much.  
  2. Select points that are NOT collinear.  The center of the map is the most true so putting a point there is a good start and around the corners.  
  3. Five reference points is really enough.  
    1. Whether judging by ArcMaps calculated degree of error or eyeballing it more than five points really is not needed.  Especially with data like the government supplied photos of Austin.
    2. Be practical.  You can get a degree of error down to 2 feet from 15 feet if you want to and are diligent about referencing.  But for the purpose these maps are being used for there would simply be no reason so.
  4. Georeference chimneys.  Any landmark that doesnt move is good to reference.  Most of my most accurate maps came from referencing chimneys.  






Monday, May 5, 2014

GISc: Science or Tool?

Is GIS a science or a tool.  Take either side. 

Taking a side on whether GISc is a Science or a tool is akin to choosing whether a pen asserts is value in that it can write or by merit of what it has written.  And to be clear, it , the pen, writes only what the pen holder can imagine within the parameters of its utility, those parameters being the amount of ink at disposal, the intensity of ink flow, the shape of the dispenser, ballpoint or otherwise, as well as the medium on which it stains.  If this were a debate to be defended and one was forced to emphasize which aspect of the pen is most noteworthy or most important  to its denotative existence it seems that we’d only end up in a contradictory landscape of the “either or”.  Ergo, GISc might neither be a tool nor a science and yet both a tool and a science; integral to itself in both regards.  For what use is a tool that has no purpose and what use is a purpose for which one has no tools?  One might concede that the tool is fundamental to having the science, but if they thought a little more would have to admit there is a science to creating the tool in the first place, on and on ad infinitum.  So where does that leave us? 

Well according to the University of North Dakota,

Geographic Information Science (GISc) is the foundation of Geographic Information Systems (GIS). It is the general term for mapping technologies used by business, government, and education.  

GISc integrates spatial data sets in the form of:

digital maps
digital aerial photos
remotely sensed imagery
global positioning system (GPS) coordinates

The technologies are used to assess, plan, and manage many facets of society, including:

agriculture
population growth
natural resource management
economic development
energy production and transmission
air and water pollution
business marketing and site location
access to medical care
city planning
building design
urban infrastructure

So, as a nominal reference alone, GISc as a term is a direct reference to the set of “technologies,” or tools to be consistent, that allow for the assessment, planning and management of this abbreviated list of facets, via the creation of data-laden maps.  To reiterate the interdependency of tool to science, however, how would GISc as a tool be relevant without the input of how society wants to use it for these applications?  This point alone leads one to see that GISc is more of a science than a tool.  And the tools that are needed to create its infrastructure are ultimately abstract ideas humans have about how to represent society in two dimensions. 

Then again, tools aren’t necessarily tangible, but at the same time, everything is tangible.  Even ideas, which seem to be intangible, are the output of atomic neural firings which become amplified audibly or otherwise as stimuli to the receptors of anyone or thing consciously or subconsciously receiving.  That would imply all of science is absolutely dependent on the tools of even  and especially our constantly evolving biology towards this techno-sphere of modern times.  So the question remains, is GISc a science or a tool?  In itself, which is to say, absolutely stagnant and without consideration of past nor future, only in what exists of GISc on a hard drive, right in this instant, it must be a tool.  To become a science GISc would require the input of data manipulators - people - at which point, it is no longer “GISc” on its own, but GISc in action, whereby it becomes a scientific process. 


If this has finally been settled, we haven’t really gotten anywhere other than exhausting the fact that we can all agree that GISc is a tool  and that we as GISc participants can continue to scientifically, and even artistically, further its utility as such for ongoingly grasping the relationships of the topographic world, entirely relevant, as that captures the majority of that which can be represented. 

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