Todd Mitchell
GEOG-499c
Lab
2: Digitizing
|
Answers
to Lab Questions: |
1. What is feature class? What is the relationship among feature
class, Shapefile,
geodatabases, coverages, and feature data sets?
A feature
class is a group of points, lines or polygons representing geographic features
of the same type, like rivers or countries. A shapefile is a single feature class. Geodatabases and coverages are ësetsí of feature classes, although each
represents features in different ways.
2. What is the advantage of Geodatabase?
What are the operations can you do with
Geodatabase in ArcGIS? What is
the difference between Personal and Multiuser
Geodatabase?
They can store
multiple feature classes, they can store labels as annotation and they have the
ability to create domains for attributes ñ establishing valid ranges for an
attribute field and minimizing entry error. Coverages and shapefiles can be imported into the geodatabase.
The Personal Geodatabase is designed to store small amounts of data (up to 2 Gigabytes) and although
accessible by several users, it can only be edited by one person at a
time. A Multiuser Geodatabase has no size limit, it permits simultaneous editing by different users and works with relational
database management systems (Oracle, Informix, MS SQL Server, etc.)
3. Is the ìSurface typeî a possible valid name for a field in a
newly created feature
class? Why?
No. The space is not allowed. An underscore (Surface_type)
would suffice.
4. What is a domain? What are the major domain types? Where can
they be used
respectively? Give an
example for each.
A domain
establishes valid values or ranges of values for an attribute field. There are Range Domains
and Coded Value Domains. A Range Domain is a valid range
of values for quantity attributes, whereas a Coded Value Domain is used when
attributes are best defined as a list (text, date, descriptive numbers). An example for this exercise
would be the length of a water line (range) and where it is located (coded
value.)
5. What are edges and vertices?
Vertices are
points in a line where the line changes direction or is intersected by another
line. Edges are the segments between
vertices.
6. What are the first and last steps for editing features? What are
the necessary
things to do
after starting editing?
Editing starts
by clicking ëStart Editingí in the Editor toolbar. Editing ends by clicking ëStop Editingí in
the Editor toolbar. Task and Target must be specified so that the required operation and the
target layer are selected.
7. What are the major tools available in Sketch tools? What are
their purposes?
The digitizing
features in the contextual menu include ëDirectioní, ëLengthí, ëParallelí,
ëPerpendicularí, and ëSnap To Featureí. These help to direct edges, define their
length, define orientation and orient a digitized vertex, edge or endpoint to
an existing feature.
8. What is the purpose for setting up snapping environments when
digitizing?
Snapping
environments help to ëdirectí a digitized feature to the existing feature when
the existing feature is within a tolerance. This greatly reduces digitizing error.
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