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AI and GIS for Beginners

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#1
dootiebubble

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I'm not a cartographer. I'm a political scientist. My dissertation research took me to Ghana to study political parties. While I was there I collected constituency maps for every national election (they range from 38 seats to 230). I've digitized the maps and transformed them into .ai files in illustrator. I've made several maps that look nice depicting election results. For instance a constituency won overwhelmingly by a political party will be colored black but one in which they barely got any votes will be nearly white.

In Illustrator (CS2) it takes several hours to fill in each constituency. I take the election results in SPSS and transform them into a number between 0 and 255 to conform to the RGB color scale. Then I take the paintbucket in AI and handfill each constituency. A librarian told me I could use GIS to make this job a lot easier so I purchased a year long student edition of ArcGIS but I can't figure it out at all.

Any advice or step by step hand holding anyone can offer would be much appreciated.

#2
frax

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maybe a GIS book, ESRI's virtual campus or the help-files would be where you should turn -- this is very basic and fundamental GIS.

For starters you would need the spatial data (the map data) -- which is the administrative regions in Ghana. You can check the admin00 dataset on the "ESRI data & maps" CD that you got with the software (I think), and how good that data is. Otherwise you could look at VMAP0 (from NGA), but their VPF format is not easy to work with.

In the adminstrative regions dataset (whichever you choose) you will see that each region in Ghana has some sort of code, which should be a letter designation or a number.

The next step is to get your election data in order. Work with this in an Access database or an excel sheet (you will need to save to CSV to be able to work with it in Arcmap). Here you need to add a column with the exact same code for the regions that you identified previously.

In ArcMap you now display the regions, and then you create a join (like a database join) to the election data, then those columns will be available for map display as categories (on the symbology tab I think). For this step, you can refer to the help file, look for "join".

For starters -- to learn how to do this -- bring up a dataset (from the above CD) with US states, and get some data (population? statistics?) for the states with the two-letter code, and experiment with joining and displaying it.

good luck!
Hugo Ahlenius
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#3
Matthew Hampton

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This is reptitive of Frax's - but different.

Like Frax mentioned - first you need some GIS data to load into ArcGIS and you can download data for Ghana here. You might need to look in the HELP for info on importing a compressed format (E00 = Export Interchange file) and use the appropriate tools in ArcGIS.

Then you need to code your data such that you have a unique ID in one column that corresponds to the unique ID from the table associated each constituency in the GIS data. Join your data (I commonly export files from Excel into dbf(iv) format for import into ArcGIS) to the GIS data based on the unique ID's.

To save some yourself some potential anguish you might also ask (hire) someone from your institution to help get things set-up initially for your particular use. It sounds quite interesting.

Oregon Metro - Portland, OR
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#4
frax

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and dootie -- unfortunately it is not very easy for you to reuse what you have digitzed in Illustrator already. Since those are seen, from a GIS perspective, as just simple drawings without any spatial registration(coordinates, projection) or topology (attributes for the polygons).
Hugo Ahlenius
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#5
Rob

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I take the election results in SPSS and transform them into a number between 0 and 255 to conform to the RGB color scale.


Dootie, you should also learn about data classification. Your above method will not hold water. Check out Slocum's book in the library for more info on a better way to approach this.

rj

#6
mike

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so you essentially have 256 classes to categorize your results? can you tell the difference between class 127 and 128 using just your eye? if you can not, then your map will not effectively convey the information. try even just 10 classes and you will see that it will start being difficult to distinguish the colors between classes (in a sequential color scheme). pick up some books, like Borden Dent's Cartography: Thematic Map Design. But definitely take some of the ESRI Virtual campus courses. they will help you get around the software.




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