Chapter 1 Flashcards
Map data falls in to two categories= ______ and ______
define both categories
discrete and continuous
Discrete data: objects in the real world with specific locations or boundaries, such as cities and roads
Continuous data: represent a quantity that is measured and recorded everywhere over a surface, such as temp or elevation
two basic approaches to data formatting are _____ model and _______ model
define both
vector and raster
vector: is designed to store discrete data
raster: is designed to store continuous data
.both data systems are georeferenced
X and Y coordinates are the ____ data while the information being represented is the _____ data
spatial
attribute
georeference
meaning that information is tied to a specific location on earths surface using X and Y coordinates defined in a standard way: a coordinate system
Vector Model
Benefits of the model(5)
Drawback of the model(2)
.use a series of X and Y locations to store information
-use points, lines, and polygons called features
.two basic bector models: spaghetti and topological
-spaghetti stores features of the file as independent objects, unrelated to each other
-spaghetti is simple and straightforward and is found in many applications
-often used to transfer vector features from one GIS system to another
-topological data model stores features, but it also contains information about how the features are spatially related to each other
-saves time when this information is needed, rather than having to use computer algorithms to determine it like in spaghetti
-topology can be used to model real world behaviour of features
- it can store individual features, such as roads and parcels, with a high degree of precision
- the linked attribute table provides great flexibility in the number and the type of attributes that can be stored about each feature
- is ideally suited to mapmaking because of the high precision and detail of features that can be obtained
- compact way of storing data, 1/10th of the space of a raster with similar info
- ideally suited to certain analysis problems, such as determining perimeter and areas, detecting whether features overlap, and modelling flow through networks
- it is poorly adapted to storing continuous surfaces/data, such as elevation or precipitation
- contour lines can be used to represent surfaces, but calculating derived information from contours, such as slope, flow, direction, and aspect is difficult - some types of analysis are more time consuming to perform with vectors
Features in Vector
Points, lines, and Polygons
.points have no dimension, a well
.lines represent objects in one dimension, such as road or utility line
.Polygons are used to represent 2 dimensional areas, such as a land parcel or state
node
vertex
.the endpoints of a line are termed nodes
.vertex is each intermediate point between nodes
a polygon is a group of _____ that define a closed area
vertices
feature classes
Attributes
like features which are grouped together into data sets
-can contain only one kind of geometry (point,line,or polygon features)
roads and rivers are different types of features and would be stored in separate feature classes
Attribute(stored in tables): objects in feature classes have information stored about them, such as their names or populations
A special field called _____ ID or _____ ID links spatial data with attributes
Feature or Object
Describe attribute table
Each feature’s attributes are stored in one row of the table, and each column has a different type of information, such as population or area
.a river or highway
thematic mapping
feature datasets
to create a map in which the states are coloured based on an attribute field, such as population
can contain multiple feature classes that are in some way related to one another ex: feature class called Transportation could include roads, traffic lights, railroads
Adjacency
Connectivity
Overlap
Intersection
logical consistency
when two parcels share a common boundary
whether two water lines are attached to each other
whether a company sprayed pesticide over the same area on two different occasions
whether a highway connects to a crossroad or has an overpass
an application of topology which evaluates whether a data model or data set accurately represents the real world relationships between features
ex: lines representing streets should connect if the roads they represent meet
ex: two adjacent states must share a common boundary that is exactly the same, even though the states are stored in the data model as two separate features with two boundaries that coincide
ex: a line or a polygon boundary should not cross over itself
Raster Model
two drawbacks of raster
.benefit of simplicity
.spatial data is represented as a series of small squares, called cells or pixels
-each pixel contains a single attribute
.vector features can be converted to raster format by selecting a single attribute to be stored in the cells
-rasters that store vector features in a raster format are sometimes called discrete rasters
.raster excels at storing continuous data
.it is possible to calculate the coordinates of every other pixel based on its row and column position
.they suffer from tradeoffs between precision and storage space to a greater extent than vectors do
.they can store only one numeric attribute per raster, while vector can store 100s
rasters that store vector features in a raster format are sometimes called _____ rasters
discrete
