Using Data from the WWW in a GIS:
How are wetlands related to other geographic features?

Shawn Vehe
University of Nebraska at Omaha
Department of Geography/Geology- Graduate Student
Omaha, NE 68182
5-97


smvehe@2access.com


Table of Contents

Introduction
Finding and Downloading the Data
Using the Data in ArcView 3.0
Resulting Maps and Analysis
Publishing this paper and ArcView3.0 maps to the web
Problems
Conclusion
Quick guide to downloading WWW data and displaying in ArcView 3.0 with a PC


Introduction

With the popularity of GIS steadily increasing, many government agencies are focusing their time, money, and energy on converting their paper maps into digital data. Digital data takes up less physical space than paper maps and is also more easily distributed. Although much of this data can be purchased from government or other private agencies and sent on a CD-ROM, one of the newest, easiest, and most popular ways to distribute this data is via the World Wide Web at no cost to the user. With so many sites on the web, it would seem that finding the needed data would be difficult and time consuming. Also, how can this data be downloaded and displayed? Other related questions include, what data is available and how can it be related to other data? The following document will explain the procedures involved in getting data from the web into a GIS, specifically ArcView 3.0. The results of this effort produced maps that will allow for an analysis of National Wetlands in the Ralston, Nebraska area compared to other physical features of the landscape.


Finding and Downloading the Data

To find my data I used Netscape Navigator and several different search engines. The best data is usually available on government agencies' web sites. All of my data was downloaded from the Nebraska Natural Resources Commission Data Bank. For other data, including links to each state's data banks, try The Guide to Mostly Free Geospatial Data.

After finding your site and the data you want to download, make sure the data is in a format compatible with your system. Much of the data is in a format with the file extensions .tgz or .tar. This is for the UNIX operating system. Often, there is an option on a webpage to request specific data to meet your needs. I had to request National Wetlands Inventory data in PC format. My request was replied to immediately as I was contacted via e-mail and given the address where my requested data was placed and could be downloaded from a ftp site. For a PC, the easiest format is ArcExport with the file extension .e00. The file may also end in .exe. This is because much of the data has been compressed to save downloading time. It is important to save the data in its own folder because during the extraction process, new files are inflated and added to the file. To decompress data ending in .exe on a PC, double click the file name. A MS-DOS window will open. When the file has completed the decompression, it will say "finished" in the top bar of the window. You will now have many new files, including one that ends in .e00. Now the data is ready to be imported into ArcView 3.0.

For my project, I used the following data files:

All of these files had excellent metadata associated with them. Metadata is important because it contains useful information such as projection, date completed, contact persons for questions, and keys to the legend.


Using the Data in ArcView 3.0

ArcView3.0, a popular GIS software, is produced by ESRI. ESRI, out of Redlands, CA., also manufactures the more powerful ArcInfo. I chose to use ArcView because although it does not have the analytical and database management features of ArcInfo, it is much easier to learn to use and can be run on a PC. ArcInfo, usually run on the UNIX system is command line driven, while ArcView is more of a "click and point" environment. My PC has 16mb of RAM. At times, ArcView ran rather slowly. For best results, I would recommend at least 32mb.

To get the downloaded data into ArcView, the data needs to be imported with the program called Import71, which is part of the ESRI ArcView 3.0 software. After Import71 has been opened, the program will ask for the "Export Filename." This is simply the name of the file you wish to import. It will end with the file extension .e00, but it is not necessary to type this in, as the program will automatically add it to the end of the file. Next, the program wants to know the "Output Data Source". This is the directory path and name of the new "feature data source" that will be created with the program. Now, open ArcView and double click on the "View" option. This will open a new view to display your work in. From the toolbar, select the "Add Theme" option. The Add Theme button is located in the top row, the second from the left, and has a plus sign on it. When the dialog box comes up, select your newly created feature data source and close the dialog box. ArcView has now added your theme to the view. The theme will not appear on the map, however, until a checkmark is placed in the box to the left of the theme name. The map should now draw out onto the screen. More than one theme can be added in this manner. Even if they are different geographies, for example one theme is a county and another a quad sheet, ArcView will place the themes in the correct location as long as they are in the same projection. If not, the projection will need to be changed in ArcInfo prior to importing into ArcView. At this point, the legend can be edited by double clicking near the theme name. There are five ways of displaying the data: Single Point, Unique Value, Graduated Color, Graduated Symbol, and Chart. Depending on the method you choose, there may be the option of reclassifying the data. From the legend editor, you can also change the colors used on the map. For example, if you are overlaying two different themes, you may need to make one of the themes the background, with solid colors representing the different values. The theme on top can then be displayed as tranparent values with a visible outline. On the left side of the View screen you can change the order that your themes will be displayed in. Simply drag the theme to the top of the View screen, this will make the theme draw last and be placed on top of the other themes in the view. After you are satisfied with the view, to print the map and add any titles or other text, double click on the "layout" option. Layout will allow you to create a map that can be printed, complete with legend, title, and neatline.


Resulting Maps and Analysis

All maps with file extension .pdf must be viewed with Adobe Acrobat Reader. Download your free copy of Acrobat Reader.


National Wetland Inventory with Stream Network.pdf

This map served two purposes: it displayed the relation of the wetlands to nearby streams and also showed the different classifications of wetlands. Wetlands are labeled using the wetlands classification system according to their modifying characteristics. Each of the letters represents a specific characteristic of the wetland. In the Ralston quad area, the wetlands were rather small areas, and mainly Palustrine wetlands. It is necessary to zoom in to see the different color values to determine the type of wetland. I was surprised to find that many of the wetlands were not associated with a stream. Being from the Ralston area, I was not aware that these other wetland areas existed. This map was created by overlaying the Ralston Quad NWI data and the Missouri River Drainage Area Stream data.


National Wetland Inventory with Stream Network and Street Files.pdf

For this map, I did not show the different wetland classifications. Instead, all of the wetland areas have been filled in red. The gray background area indicates the extent of the Ralston Quad, with the blue lines representing streams and the black, streets. As expected, most of the wetland areas were not located in areas with a concentrated street network. This map was created using the Ralston Quad NWI data, the Missouri River Drainage Area Streams, and the Douglas and Sarpy County Tiger Street Files.


National Wetland Inventory with Land Use.gif

I chose to display this map in a .gif format because the map did not need to be zoomable as the details were not as small. The Ralston Quad presents any interesting study. At the north end of the quad (in Douglas County), the land is mostly urbanized. In the south (in Sarpy County), much of the land is used for agriculture. Perhaps most puzzling, is the the occurence of many wetland areas in land labeled as dry cropland. If the land is dry, it would be interesting to find out the source of water for these wetlands. After checking with the first map (wetland classification + streams), I found that several of these wetlands were identified as palustrine, unconsolidated bottom, semipermanently flooded, diked or impounded wetlands. The fact that the wetlands were not naturally occurring offers part of the explanation. One of the problems with this map is that it was created from a raster based map, so the landuse patterns are in obvious pixel squares. The even pixel-based boundaries that exist on the map, do not exist in real life. Since each pixel resolution is probably classified as the majority landuse that occurs, this could be the source for inaccuracies. For example, there are several rectangular and square areas identified as water. On the earth's surface, it is safe to assume that the water area is irregularly shaped. Also, there is not a straight edge boundary between water and dry cropland as indicated by the map. This map was created by overlaying the Ralston Quad NWI with the Missouri River Drainage Area Streams, and the Douglas and Sarpy Counties Landuse.


National Wetland Inventory with Soils

There is no printed or viewable map associated with this study because there were too many different soil types represented. I was unable to select unique colors to display each of the different soil types. This is a situation where the best analysis is performed on the computer screen. I could determine all the areas where a soil type was located by querying the data. It was also helpful to use the identify function. This was much more effective than the overall map. I found that the wetlands were not located in any particular soil types. Also, many of the areas classified by the soil survey as wet alluvial land were not classified as wetlands in the NWI. This view was created by overlaying the Ralston Quad NWI with the Missouri River Drainage Area Streams, and the Douglas and Sarpy County Soil Surveys.


Publishing this paper and ArcView maps to the web

I created this web site with the help of Netscape Navigator Gold 3.01's edit function. I found this free, downloadable program to be extremely easy to use. The online help answered any questions I had. Similar to other web publishing software, Netscape inserted all the necessary HTML code, and even published my page to the web. It also supports JAVA, VRML, and other more advanced programming.

The maps that were created in the layout function of ArcView, covered a fairly large area. Typically, maps are displayed as .gif or .jpeg images. I did not feel that these image files would allow the viewer to zoom in close enough to see the small details of two of my maps. The solution was Adobe Acrobat's PDF (portable document format), which is multi-platform and zoomable. Similar to a post script file, a PDF contains the instructions explaining how to print and display an image or document. Because I did not have this program on my PC, from the layout screen on ArcView, I chose the export to postscript function from beneath the file menu. At the Cartography Lab at UNO, I opened the exported postscript files in Adobe Illustrator. Then I printed the files to a PDF file and saved to my disk. I was then able to copy the pdf files from my disk onto my PC and finally, onto this web page. The only problem with this process was that I was unable to change my landuse map into a .pdf. When I tried to open the landuse.pdf, some of the data was missing. I am assuming this was a large file size and memory problem. I changed this map into a .gif image.


Problems

Most of the problems in this study were caused by the fact that the wetland areas were quite small and it was difficult to find ways to display the data effectively. Also, a quad area is a fairly large area to try and depict on a 8 1/2 X 11sheet of paper or a computer monitor screen. Another problem was the layout function of ArcView. At times, it was not flexible enough to show the areas and data that I wanted to display, so I imported the map into CorelDraw, and edited from there. In general, ArcView 3.0 was fairly intuitive and easy to learn.


Conclusion

After this project, I reached an important conclusion concerning GIS. Often people question if GIS is really a geographers tool. It is possible for anyone with a computer background to download data and place it into ArcView. Perhaps the downloading and import procedures are even easier for a computer scientist than for a geographer. But the real geography lies in the analysis. To effectively use GIS to analyze spatial features of the earth it is necessary to have a background in Geography. For example, the computer scientist does not know how slope, elevation, and landuse relate to wetlands development. It takes a geographer to relate all the factors of the problem to come up with the most complete and analytical conclusion.


Quick guide to downloading WWW data and displaying in ArcView 3.0 with a PC

Please see above for more complete details.

1. Log onto the net and go to the site you wish to download from.
2. Download the file into into its own folder.
3. Decompress the data if it is in a compressed format.
4. Open ESRI ArcView's Import71.
5. In box 1, select the file you wish to import. It will end in .e00.
6. In box 2, give the file that will be created with the import function a name.
7. Open ArcView 3.0.
8. Open a new view, by double clicking on the View icon.
9. Select Add Theme from the Toolbox and choose the newly imported file.
10. Place a checkmark in the box next to your new theme.
11. Edit the legend by double clicking near the theme name.