DIGITAL LINE GRAPHS AND DIGITAL ELEVATION MODELS

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Exercise 16 - Digital Cartographic Databases

            Make a folder 'DLG' in your area and copy the files BE_HYD.DLG, BE_RD.DLG, and BLKEAR.DEM in \EXERCISE, to the DLG folder.

        Importing the DLG vector files
    Run DLG (in File/Import/US Goverment Data Formats) and input BE_RD.
    Chose Lines as type of data and ROADS as the output file.
    Choose SCAN DATA to see the major and minor codes attributed to the various line
data; choose (click the buttons for Primary route (201), Sec. Route (205), Road class 3
(209), Road class 4 (210), and Photorevised (0). Click OK to return to the previous
menu, and change the Id's for each line type (Assign New ID box), recognized from its
minor code in the Assign New ID box, to 1 (major roads), 2, 3, 4, and 5 (for
photorevised), in the `Features to Extract' box. Click OK.
    Run the Symbol Workshop (in Display) and assign a line type, colour, and thickness, to
each line type, e.g. for Primary route - red, full line, thickness 3; Secondary route -
green, broken line, thickness 2, etc, and save as a line symbol file called `roads'.
Display ROADS with the symbol file ROADS.

Follow same procedure for BE_HYD, extracting streams (only) as lines into a vector
file STREAMS (attribute value of `1'). Create a line symbol file `streams' with `1' as
blue. Extract marshes (attribute value `1') and lakes and ponds (attribute value `2') as
area (polygon) features into WATERBOD, and construct an appropriate polygon
symbol file `waterbod'.

               Importing the DEM raster files.
    Run DEMIDRIS (Files/Import/US Goverment Data Formats); import BLKEAR.DEM;
output DEM. Display with the Idrisi 256 palette, and autoscale. Check the HISTO
distribution and then set the minimum value in the .doc file to the minimum non
background value [218]; in this case querying the cell values will give the real elevation
values and not the palette value [0-255]). Change the colour number 0 in the idrisi256
pallete to white and save as a BLKEARTH palette file. Display the image with the new
palette.
    Layer ROADS over DEMC. The raster and vector images are not registered because
DEMC is a NAD83 datum image and ROADS is a UTM NAD27 datum image.

Exercise 17 - Changing the Reference system with PROJECT

Run PROJECT (in Reformat) and input STREAMS; use STREAMS83 as the
output file name, and US83TM16 as the output reference system. Same for ROADS and
WATERBOD.
Read page 13-105 regarding the error characteristics of the UTM coordinate system.

FIGURES

Figure 1. Plate Tectonics.

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