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I need help symbolizing small scale wetlands layers

March 29 2011 | 3 comments
Categories: Map Data

Help! I'm trying to create a larger poster size map of Michigan. I need to show wetlands in a similar way as the USGS topo's, and the best layer available seems to be the NWI. The problem is that it is super detailed. I don't need to know individual attributes, just weather it is a wetland or not. My problem is that the NWI is so detailed that when i zoom out to the scale required to show all of Michigan it is too detailed. I need a courser or more generalized data layer. Does anything like this exist? What I need is very similar to the online NFWS map viewers generalized layers when they are showing it at a very small scale.

any help?

Thanks,
Cam

Mapping Center Answer:

Try using instead the National Land Cover Dataset (NLCD) -- this includes a Wetlands category that is further subdivided into Woody and Emergent Herbaceous Wetlands.  Here is the link to the online data: http://www.epa.gov/mrlc/nlcd-2001.html.

Here is a link to the classification system they use for the land use/land cover categories: http://www.epa.gov/mrlc/classification.html

A couple of problems with that data posted by Cameron Fuess on Mar 30 2011 6:48AM
So... thanks for the quick response. I looked at that data set and I had a couple of problems with it;
1. It looks more detailed even then the NWI?
2. It's a raster and I'm looking for a vector. Is there another way to view this data as a vector?
3. Worst of all, the data download site is not working currently. This always makes it difficult!


Thanks for the help,
Cam
NLCD for 24K maps posted by Aileen Buckley on Mar 30 2011 8:10AM
You are right -- NLCD is about the right resolution for 1:24,000 scale maps but because it is raster, I find it easier to generalize. That the web site is working is something else altogether (but it did make me chuckle this morning!)

Now on to the serious stuff - wetlands, especially riparian wetlands, are a kind of thing that exists to a large degree only in small areas. Getting courser resolution data for a larger area will not make them show up at smaller map scales. They just do not exist over large areas (for the most part). It's the same thing as trying to make a state-level map of, say, California, to show potential tsunami inundation areas. Those areas only exist along the coast and you have to see them at larger map scales to see the detail. They just won't show up on a map of the whole state on a page size of 8 1/2 x 11 inches.

If you HAVE to make a state-level map of the wetlands, then maybe you should reconsider your approach. Maybe instead you show the detail for sections of the state where they DO exist and you use the state extent map to show the location of your inset maps that show the wetlands at larger map scales. Or you can increase the size of the paper to show the map at a larger scale (but then you have to deal with the large expanses of space in which there are no wetlands and the map is sparse.)

Or you can keep going down the path you are currently following. There was an older (1970s based) USGS 1:250K land cover data set called LUDA (Land Use Data Acquisition). I haven't used it in years so I don't know what the status of it is. If I recall right, it had wetlands as one of the classes. Of course, it is terribly out of date.

Or you could try to use a surrogate for wetlands, like hydric soils (soil are one of the three main components used to determine wetlands; the others are vegetation and hydrology). Soils data are available at 1:20K (SSURGO) and 1:500K (STATSGO), although I doubt you will find much of use in the STATSGO data to help you map wetlands, but you could check.

Back to the fundamental issue -- you are faced with the challenge of mapping a phenomena that exists primarily over small extents for an area that covers a large extent. A single poster-sized map may not be your best solution.
NHD data for swamps/marshes posted by Aileen Buckley on Mar 30 2011 9:45AM
I was reminded today that the National Hydrography Dataset (NHD) contains a category for swamps/marshes. (There is also a category for Inundated Areas - you would have to check their definition to see exactly what this means.) I am not sure if you have to map wetlands per se (a political theme, to be sure!), but maybe swamps/marshes will suffice as a substitute. The NHD data are available at high, medium and low resolutions. Here is the link to the NHD web site: http://nhd.usgs.gov/data.html.

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