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54 Cards in this Set

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Nodes

End points of lines

Vertices

Point locations along a line

Accuracy

How close a measured value is to the true value

Precision

How close the measured values are to each other.

Vector Topology

Enforce strict connectivity and recording adjacency and planarity. Creates an intersection and places a node at each line crossing, record connectivity and adjacency. Maintains information on the relationships between and among points, lines, and polygons in spatial data. Greatly improves the speed, accuracy, and utility of many spatial data operations. Do not change: invariant property (polygon adjacency, connectivity. There is no single, uniform set of topological relationships that are included in all topological data models--> different researchers/ software vendors have incorporated different topological information on their data structures.

Planar Topology

Requires that all features occur on a two dimensional surface. There can be no overlaps among lines or polygons in the same layer. When planar topology is enforced, lines may not cross over or under other lines. At each line crossing there must be an intersection.

Adjacency

Which polygons are next to which.



Connectivity

Which lines connect to which.

Topological constructs besides planarity

Polygons may be exhaustive-no gaps, holes, or islands.




Line direction may be recorded-a "from" and "to" node are identified in each line. Directionality aids the representation of river or street networks, where there may be a natural flow direction.




Some GIS software creates and maintains detailed topological relationships in their data which results in more complex and perhaps larger data structures, but access is often faster, and topology provides more consistent "cleaner" data. Other systems maintain little topological information in the data structure, but compute and act upon topology as needed during specific processing.

Topological Constraints

Topology can be specified between layers when we want to enforce spatial relationships between entities that are stored in different layers. For example, property lines vs building footprints: rules may be specified that prevents building footprints from crossing property lines.

Dangles

Lines that do not connect to other lines. May be proscribed or limited ro be greater or less than some threshold length.

Topological Data Models

Often used codes and tables to record topology. Nodes and lines are given a unique identifier. Sequences of which are recorded as a list of identifiers, with point, line, and polygon topology recorded in a set of tables.




Many GIS systems are written so that topological tools are provided to ensure the creation and maintenance of topology but that the coding is not visible to users, nor directly accessible by them. Tables that these commands build are often quite large, complex, and linked in an obscure way, and therefore hidden from users.




Greatly enhance:


Many vector data operations. Adjacency analyses are reduced to a quick table look up (quick and easy)


Other spatial data operations. Network and other connectivity analyses are connected with the flow of resources through defined pathways.


Explicitly record the connections of a set of pathways and facilitate network analyses.


Overlay operations.

Point topology

Points are individual of each other.


Points may be recorded as individual identifiers with coordinates included and with no particular order.

Line topology

Includes substantial structure. At minimum, identifies beginning and ending points of each line. Variables record the topology in a table. Variables such as line identifier and starting and ending nodes for each line. Lines may be assigned a direction. The polygons to the left and right of the line are recorded.

Polygon topology

Defined by tables that record polygon identifiers and the list of connected lines that define the polygon. Edge lines are often recorded in sequential order. The line for a polygon form a closed loop and thus the starting node of the first line in the list also serves as the ending node for the last line in the list.

Limitations and disadvantages to topological vector models

Computational costs in defining the topological structure of a vector layer --> costs are modest




Software must determine the connectivity and adjacency information, assign codes, and build topological tables.




The data must be "clean". All lines must begin and end with a node, all lines must connect correctly, and all polygons must be closed. Unconnected lines or unclosed polygons will cause errors during analyses.




Human effort required to ensure clean vector data because each line and polygon must be checked and edited as needed to correct errors.

Buffer

Region less than or equal to a specified distance from one or more features. Can be created for point, line or area features. It is a proximity function.

When you want to find out which counties are crossed by Route 66 you would use which of the following?

Intersect Tool

For a cadastral database to be topologically correct it is best if adjacent polygons:

do not cross the cadestral layer. The cadestral layer is the property lines layer. The adjacent layers would be the buildings layer.

Raster data models

Elevation, mean temperature, slope, average rainfall, cumulative ozone exposure, soil moisture. Since raster data uses cells, it is used for variables that change continuously across a region.

A raster's size is a function of

cell size

Referencing a Raster in ArcGIS. What tool?

Mosiac/Mosaic to a new Raster

A 1000 by 1000 raster which is resampled to a 10 by 10 raster would reduce the overall number of cells by

1000*1000=1,000,000


10*10=100


1,000,000-100=


999,900 cells

TIN Models

Triangulated Irregular Networks. Commonly used to represent terrain heights. X Y and X points used to create triangles. Each triangle defines a terrain surface, assumed to be of uniform shape and slope. Uses some form of indexing to connect neighboring points. Triangular point connections continue reclusively. TIN's are more complicated than a raster grid. Can be more appropriate and efficient when storing terrain data in areas with variable, discontinuous or bumpy terrains. The differences in sampling densities results in more points, which results in smaller triangles in the densely sampled areas. TIN's preserve measurement at each location.

Spatial Analysis Operations may produce

A solution to a problem such as identify a high crime area or generate a list of roads that need repaving. The selection of the best location for a new business. An output that can be used as the input of the next operation. Slope (how steep each cell is). Aspect (slope direction). New Data layers. Spatial outputs with no geometric data attached. A scalar value. A list. A table

Terms associated with Spatial Analysis Operations Scale

Local, neighborhood, and global.

When you do a ________ spatial operation you use data from a selected section of the surrounding area (but not the whole data layer)

neighborhood

Boolean Operation

Associated with the terms AND, OR, and NOT.

In Spatial Selection when you want to identify features that touch one another you would use

Adjacency

In Spatial Selection when you want to identify features that are within another feature class you would use

Containment

A spatial join

uses location criterion to join features with no change in geometry of features. A spatial join involves matching rows from the Join Features to the Target Features based on their relative spatial locations.

Which vector overlay function works like a “cookie cutter”

Clip

Slivers are

areas where overlap or edges don’t meet. the overlaps are where there are topological errors, or layers that do not align exactly

Network analysis can be used for

roads, power lines, telephone cables, water distribution systems, and stream networks.

Geocoding

Spatially referencing point features based on the address of a feature and knowledge of an address range for the linear network

By using GIS and eliminating left turns UPS reduced it’s miles traveled by

28.5 million miles per year

Geocoding tends to work poorest in

rural or less developed areas

Fixed weighting (local averaging)

Smoothes data, gives search radii, gives a moving average.

“The Further a Sample Point is Away, the Less Influence on Interpolated Points” This statement is associated with which of the following

IDW

Which of the following is not considered an Operation in Cartographic Modeling

a flowchart

An 8 bit single ban raster will give you

256 potential unique values

Which of the following raster resampling technique is best for Continuous Surfaces

Bilinear interpolation or cubic convolution

ArcMap can only display ____ of a multi band raster

3 Bands

Floating point rasters are good for

continuous, numeric data.

Cell Size Output options in the Raster Environments include

max or min of inputs/ same as layer/ as specified below

Which of the following Extent of Output options creates the output raster with an extent large enough to contain all the input rasters

union of inputs

When merging rasters it is important to choose the best method of handling overlap. Which of the following would be best for merging two rainfall rasters

Mean or blend (for continuous data)

In Raster Map Algebra the following Boolean operations will always return a Logical 0 or 1 except

No Data

According to your book Adjacency can be defined in a couple of different ways when you’re running a spatial selection operation. Would it be possible for Arizona and Colorado to be “adjacent” according your book?

Based on node adjacency rather than line adjacency.

When combining a Floating Point Raster and an Integer Raster you get

Integer Grid

Proximity function

Buffer, near tool, multiple ring buffer, create thiessen polygons

Write a Boolean Expression where all the states in the data set are selected except Texas

NOt (State = Texas)

Explain the following CON statement (conditional statement).


OutRas = Con(InRas1 < 5, Sin(InRas1), Con(InRas1 < 20, Cos(InRas1), Con(InRas1 > 50, 100, 0)))

For values less than 5, the sine is calculated. For values less than 20 but greater than 5 the cosine is calculated. For values greater than 50, 100 will be assigned and all other values are assigned a value of 0 (false)

If the value of a cell in an Input Raster is less than 20, 10 should be assigned to that cell location (true) on the output raster; otherwise, the cell values greater than or equal to 20 will be assigned 1 (false) on the output raster

OutRas = Con(InRas < 20, 10, 1)