CSS 4200 Name: _____________________
Geographic Information Systems
Fall 2008 Due (#3.2): Week of September 29th.
Lab Assignment #3.2: Map Digitizing and Editing
Part 3. Clipping maps using the clip_map geodatabase
In this part of Lab#3, we will all edit the same map using ArcMap.
3.1 In ArcCatalog, Copy the land cover coverage (‘ielulc’) from the class data Lab 3
folder (N:\Data\Lab3) to your project directory.
3.2In ArcMap add the ‘ielulc’ coverage from your project directory and the ‘clip’ feature
class that you generated in Part 3.1. You will notice that ‘ielulc’ has many
polygons that extend outside the quadrangle (“clip”) boundaries. The “Clip”
function will use ‘clip’ like a cookie-cutter to cut off the excess polygons. All
attributes of ‘ielulc’ will be preserved.
3.3To clip in ArcGIS, open the ArcToolbox, and select the Index tab at the bottom.
Type in Clip, double click on “Clip (analysis)” and the Clip tool will automatically
open. (The index tab is a great way to find a tool without having to search through
all of the toolboxes.) Another way to get to the Clip tool is through the ArcToolbox
window under Analysis Tools/Extract/Clip. Once you have the Clip tool open,
select the appropriate input layer and clip layer. Name the output layer “land_clip”
and make sure it will be created in your project directory. The output file “land_clip”
is in shapefile (.shp) format. To better understand the tool, click the show help tab
in the lower right hand corner of the window. (This feature is also available in most
other tools, and is a useful illustration of how tools operate.)
After you clipped ‘ielulc polygon’ to create ‘land_clip’, right-click on ‘land_clip’ and
Open Attribute Table, select the ‘AREA’ field, right-click and choose ‘Calculate
Geometry.’ After calculating geometry, confirm the area of ‘land_clip’ is correct (same
area as ‘clip’) before proceeding to the next step. Use ‘Σ Statistics…’ which is accessed
by right-clicking on the ‘AREA’ field.
3.4We need to use ArcToolbox functions to eliminate all polygons smaller than 4047 m2
(1 acre). Using the “Eliminate” command in Arc Toolbox under Data Management
Tools/Generalization/Eliminate, eliminate all the polygons smaller than 4047 m2.
The “Eliminate” tool only works on selected data. So you will first need to select all
polygons in land_clip that are less than 4047 m2 in size. Do this by opening the
attribute table for land_clip and performing a Select by Attributes under the “Options”
tab in the lower right hand corner of the attributes box.
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