SO432, GIS Fall 2008

TIGER data and representing reality

This lab is entirely individual effort.  You can do it in your room without any problems if you download and install MICRODEM.  It will be due Tuesday 23 September 2007.

Lab objectives

• Contrast ASCII and binary storage of cartographic data.

• Understand how vector data is designed and stored.

• Understand the structure and importance of a shapefile.

References:

• The MICRODEM help file has information for both TIGER data and shape files.

• If you want more information:

  • Reading on TIGER data: http://www.cs.nyu.edu/~yap/classes/modeling/01s/lect/l52/l.html   Do not try the exercises on this page, but read to get an understanding of the encoding.

  • Shape file technical description: http://www.esri.com/library/whitepapers/pdfs/shapefile.pdf (probably more than you need to read).

The file c:\mapdata\tiger\tiger_cfcc.dbf on the hard disks in the lab (open it with the DB button in MICRODEM or Excel) has definitions of the CFCC codes.  The file is also at http://www.usna.edu/Users/oceano/pguth/microdem/win32/tiger_cfcc.dbf

• Get the FIPS code for your county at http://www.epa.gov/enviro/html/codes/state.html.
• Get TIGER data in the native TIGER format for your county at http://www.census.gov/geo/www/tiger/tiger2006se/tgr2006se.html   Save this on the hard disk and remember where you put it. You should put it in a subdirectory under c:\mapdata\tiger\XX, where XX is the abbreviation for your state.   You might have to create this subdirectory.
  • Unzip the TIGER file. You can have Windows do this, or you can use MICRODEM (the data manipulation form, Uncompress, ZIP menu option).
  • We will look only at the RT1 and RT2 files. Open them in Word. Note they are ASCII files, and you can "read" them in Word or a similar program.
  • Open the file with the "Open, Tiger County Map" to open a map.
• Get the TIGER data for the roads, as an ESRI shapefile, from http://www.census.gov/geo/www/tiger/tgrshp2007/tgrshp2007.html   You want the download for a single county. You should put it in a separate subdirectory, different than the native TIGER files, so you can keep track of multiple files.
  • Unzip the file.
  • Look at the file in MICRODEM.  Use the "File, Open shape file map" menu option.  You can zoom in and use the graphical power of the GIS program.

Native TIGER Format:

In the RT1 file, find the record (this might be a block) that includes your home, paste it into your lab report, and fill in the table below:

In the RT2 file, are there additional coordinates for your record? How could you tell?

If you block does not have a continuation record, find another record that does and fill in the table for that record.

How many additional coordinates can there be in the RT2 file? What else (if anything) is in the RT2 file? How can you go between the RT1 and RT2 files?

What other kinds of records (besides roads) are in the RT1 file? How could you tell?  You can use the TIGER Icon in MICRODEM which has an intelligent display of the RT1 and RT2 files.

ESRI Shape File:

Does the shapefile have all the information in the native TIGER file?  Does it have any additional information?  Is it missing anything in the RT1 and RT2 files?

Find the record for your block.  What are the lat/long coordinates for the record (when you find the record, you can right click on it and get the coordinates), and how do they compare with the coordinates for the record in the native TIGER format?

Where are the actual coordinates of your street stored?

Highlight your block on the map and the multi-coordinate block, and blow the map up.  Can you see the individual line segments that were digitized?

Compare the Two Formats

Briefly discuss the advantages and disadvantages of the two formats.