Understanding GIS Data-1

Question 1

What is GIS?

Answer 1

METHOD to capture, store, analyze, manipulate, visualize geographically referenced information
SYSTEM of computer hardware, software, and data and metadata
SMART MAPS linking a database to the map

Question 2

What Questions Should We ask when making a map?

Answer 2

QUESTIONS ABOUT INDIVIDUAL GEOGRAPHIC ENTITIES

• about space
• about attributes
• about time

QUESTIONS THAT ARE AMENABLE TO GIS ANALYSIS

• Q about spatial relationships
• Q about attribute relationships
• Q about temporal relationships

Question 3

What are Q that GIS cannot answer easily?

Answer 3

EXPLANATORY QUESTIONS
-why are these entities here, why do they have these attributes, why have these attributes changed?
PREDICTIVE QUESTIONS
-what will happen at this location if this happens at that location?

Question 4

How do maps potray the world?

Answer 4

Through:
POINT FEATURES
LINE FEATURES
POLYGON FEATURES
ANNOTATION FEATURES

Question 5

What are the two types of map information?

Answer 5

Discrete or Continuous

Question 6

What is Generalization and Scale

Answer 6

SCALE: the ratio of size on the ground to size on the map. scale influences the generalization of features

Question 7

What are the two different types of GIS data models?

Answer 7

VECTOR MODEL
-stored as x, y in rectangular coord system
-points lines or polygons
-FEATURES AND
ATTRIBUTES: each feature is linked to an entry in a data table that has info about its attributes
RASTER MODEL
-store surfaces/ fields of variable change continuously over space
-many potential values. adjacent cells are rarely the same value
TYPES
Discrete

Question 8

What is a feature class?

Answer 8

• collection of similar objects that have the same attributes which are stored as a single unit.
• stores spatial features with a table of associated attributes for each feature
• all features share the same table so they all must have the same attributes
• feature classes may contain only one type of geometry (points, lines or polygons)

Question 9

What are the types of vector models?

Answer 9

CORELATIONAL MODEL
-features and attributes stored separately
-are linked by a common feature ID
-is the original model for older GIS systems
OBJECT-ORIENTATED MODEL
-features and attributes are stored as a single unit
-reduces overhead in matching features to attributes
-simpler

Question 10

What are the advantages of vector models?

Answer 10

-store discrete object data, precise, stores a lot of attributes, flexible, compact storage of info, suited for certain types of analysis (areas, lengths, connections)

Question 11

What is a discrete Raster?

Answer 11

• store features but in raster format

- have relatively few values that change abruptly

Question 12

Tell me about Scanned images

Answer 12

• these are paper maps recorded on a scanner

- form rasters

Question 13

What are picture files?

Answer 13

any map picture could possibly be used as a GIS data source, however, it must be georeferenced, or registered to a known coord system before you use it in GIS

Question 14

What is the difference between a value raster and a picture raster

Answer 14

VALUE RASTER
-DEM or land use raser stores a value representing an object or quantity (ie. elevation or rainfall)
-used for analysis
PICTURE RASTER
-stores arbitrary color values that have no direct relation to quantity or attribute
-used as background pictures only

Question 15

How does resolution impact the maps?

Answer 15

• storage space increases by the square of the resolution

- when you have large areas at high precision you have a problem because detail will be lost

Question 16

Tell me about storage of attributes

Answer 16

• roads can have more attributes (speed limit, # of lanes, etc)
• every attribute needs a new raster
• we can only store numeric attributes

Question 17

Tell me about Continuous Data

Answer 17

• is faster and more flexible than vectors

- sometimes you have to use rasters