Shapefiles, Topology And Geodatabase

Question 1

How are shapefiles stored

Answer 1

.shp - shape format, feature geometries

.shx - shape index format, for efficient querying

.dbf - attribute format, attribute data

Question 2

Difference between shapefile and coverage

Answer 2

Coverages came earlier
Can edit shapefiles into impossible shapes (overlapping parcels)
Double lines in shapefiles for shared features, no shared lines in coverages
Operations run faster in coverages
Overlaps coverages cannot deal with

Question 3

What does a DBMS do?

Answer 3

A database handles storage and retrieval of data using specific protocols and methods and abstracts from the hardware or file system.

Does not usually handle locking, access eighths or views

Defines an additional later on top of the database and abstracts forms from specific methods

Question 4

What is n-tier architecture

Answer 4

N-tier aims at decoupling the different components into separate layers than can only access the next tier.

Question 5

What are characteristics of a DVMS

Answer 5

A DBMS abstracts from specifics of a database and offers additional functionality(e.g. user rights)

A software architecture abstracts from the specific DBMS and offers additional functionality (e.g. web-based access). The application server hides the storage from direct access by the user. This provides the business logicz

Question 6

How to create a database scheme

Answer 6

First form a primary key with unique value
Then add attributes (given a specific type)
Primary keys can then be used as foreign keys in another table for cross referencing

Question 7

What are primary keys, attributes and data types for?

Answer 7

Each table has a primary key, one column that has a unique value for each record in the table
Each attribute has a specific type such as integer or point. Data types restrict what kind of data can be stored in this attribute

Question 8

What is the first normal form associated with database practice

Answer 8

Only one value per attribute (cell) for each record, cells do not repeat

Question 9

What is the second normal form

Answer 9

Every non-attribute is functionally dependent on the prime key.
This creates multiple tables.
E.g creates land record 3 which associates the parcel id to owner id

Question 10

What are characteristics of third normal form

Answer 10

Every non-key attribute is non-transitively dependent on every candidate key
E.g because an owner is in a parcel, and a township is also in a parcel, then the owner is in that township - this information would not be stored together

Question 11

What is a topological data model?

Answer 11

A vector model consists of points lines and polygons to represent features on a map. Topology informs the connectivity and contiguity if interrelated points lines and polygons

Question 12

What is contiguity

Answer 12

The state of bordering or being in direct contact with something

Question 13

What is the minimum mapping unit?

Answer 13

A lower limit on the size of the objects we represent

Question 14

Point topology

Answer 14

Points are usually independent of one another and are recorded with individual identifiers with coordinates

Question 15

Line topology

Answer 15

Structure and identifies a minimum beginning and end point, may include online identifier a starting node and an end node

Question 16

Costs of vector topology

Answer 16

Software must determine the connectivity, and adjacency information, assign codes and build topological tables. Computational costs can be quite modest
Data must be clean, lines must end in a node and begin with a node, connect correctly

Question 17

Benefits of object data models

Answer 17

Discrete objects easily identifies and can inherit properties easily

Question 18

What is run length code

Answer 18

This is a data compression technique. It is based on recording sequential runs of raster cell values
E.g A7 rather than AAAAAAA

Question 19

What is a quad tree

Answer 19

A faster compression technique that combines raster values the same into one uniform area

Question 20

What are entities?

Answer 20

A collection of related data items that are treated as a unit represents an entity

Question 21

What is an instance

Answer 21

A specific entity is referred to as an instance