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Thread: Population density map

  1. #1
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    Population density map

    I've been charged with creating a population density map similar to this one: I'm having trouble figuring out how the population density is displayed on this map. It doesn't appear to be by population/square mile by census block, but by something else. How did the creator of this map create the polygons that are irregular in shape and varying intensities? It's almost like a dissolve was done on the layer? Here's my map of population/square mile by census block: Any advice on how to achieve the look of the first map? Thanks for any input.

  2. #2
    Cyburbian estromberg's avatar
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    I would imagine the author used the Spatial Analyst extension to ArcGIS. It allows you to do density calculations and whatnot.

  3. #3
    Cyburbian b3nr's avatar
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    By the looks of it i'd say he/she either had much more precise data on smaller greographical areas, or its simply been graphically touched up in some way, perhaps exported from the GIS program and done in paintshop or somthing? I know i've blurred lines before to make them more pleasing on the eye.

  4. #4
    Cyburbian Plus JNA's avatar
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    If you have
    The ESRI Guide to GIS Analysis Volume 1: Geographic Patterns & Relationships, 1999

    Look at Chapter 4: Mapping Density
    Page 81 - If you have data summarized by defined area but want to create a density surface
    Oddball
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    Broke parts take a little longer, though.
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  5. #5
    Cyburbian
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    If you can send a larger picture of the desired map, it would help.

    Otherwise, I would say it was touched up in Photoshop.

  6. #6

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    Quote Originally posted by estromberg View post
    I would imagine the author used the Spatial Analyst extension to ArcGIS. It allows you to do density calculations and whatnot.

    Exactly done in Spatial Analyst. You need the "convert vector to raster" tool available in that extension. If you've define you'e cell size to, say 10m pixels, for an area the size of this county, you would prolly get a very similar result.

    When I was with CALEPA, I used to do this stuff all the time. Now that I'm in a Land Developement firm, I don't do it as much.

    HTH

  7. #7
    Cyburbian
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    Sample Area size for the first image seems way smaller than what you've got, you won't gain much converting to raster what you have. You'd have the same image you have now, but with less precise edges. The only other way would be interpolating and generalizing the raster, that will make the edges smoother. Or using a quantitative degradation of color to represent it.

  8. #8
    Cyburbian estromberg's avatar
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    Population is available at the block level, which would make the density calculation much more accurate than using tract level data.

  9. #9
    estromberg is right about using ESRI's Spatial Analyst. Key concept here is that the first map interpolates population on a grid; the cartographer does not actually have population on a tiny geography.

    I'm afraid you might not have access to the pricey ESRI extensions that enable this task. You could investigate lower-cost GIS software, but you may just need to tell the boss it can't be done with what you've got.

    I use ESRI's Geostatistical Analyst, which has very sophisticated interpolation techniques. The image below is an interpolated raster from vector polygons. You can see the rough outline of the polygons (not the circles). I use this interpolation technique to estimate population and other statistics within differing geographies, like the circles shown.

    Here's another approach to throw by the boss: make a dot density map. ArcMap randomly places dots within a polygon to represent 'x' numbers of stuff (in this case, 10 people per dot). It doesn't require fancy software or any real interpolation. My undergrad cartography class described this technique as being originated to show the number of pigs in Tennessee in the thirties, or something. Anyway, it's appropriate, if simplistic.
    Attached Thumbnails Attached Thumbnails draft Growth Concept 07-01026gpg.jpg   Untitled-2 copy.jpg  

    Last edited by NHPlanner; 15 Jul 2008 at 12:09 PM. Reason: double reply

  10. #10
    Cyburbian
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    Definitely a raster image. Raster allows much smother transition from one value to another. could have been edited as well with PS.

    BikePlanIt, that's a good method, I'll have to try that sometime. but I don't think that's what David251 is trying to accomplish

  11. #11
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    arcGIS

    hello everyone.

    sorry to raise this old page from the dead, but i stumbled here on a google search.

    im in need of a population density map and from what i gather here, someone someplace is using arcgis information to generate it.

    i recognize that format from getting land elevations for something unrelated. if anyone could direct me to a place that has a how to, or description about how one generates such a map i would be very happy.

    thank you

  12. #12
    Cyburbian b3nr's avatar
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    Well first off you'll need the data. Then you'll need some software (Esri Arc or Mapinfo most commonly).

    Do you have those?

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