GIS

Managing Raster Data

Managing Raster Data

- divides space into discrete uniform unit squared cells
- does not provide precise locational data

Spatial resolution

reducing grid cell size to half the current size will increase data value four times

resolution

dimensions of a pixel

Whittaker-Shannon Sample Theorem

Cell size must be smaller than half of the minimum feature that you intend to represent

Continuous Rasters

o Store numeric values that can be measured anywhere
Examples: Elevation, temperature, precipitation

Discrete Rasters

Store Categorical data
Examples: land use, roads

Raster Pyramids

o May be built for a raster to speed its display
o Lower resolution copies are created

Nearest Neighbor Resampling, categorical

• Grabs value from old cell that falls at center of new cell

• Preserves original value

• __________ data

Bilinear resampling, continuous

Finds new value from four cells closest to center of new cell; ____________ data

cubic convolution resampling, continuous

finds new value from 16 cells that fall closest to center of new cell; used for ___________ data

Raster Tables

o Attribute tables are created for discrete rasters with limited number of unique values

Value Field

part of a raster table that contains each unique value

count field

indicates how many cells have that value in a raster table

Storing raster data

BIP, BIL, BSQ

BIP

Band Interleaved by Pixel

BIL

Band interleaved by line

BSQ

band sequential

Storing Raster Values

one binary digit is a bit
8 bits is one byte
number of bytes is pixel depth

Multiband Raster

contain multiple raster arrays with same number of rows, columns, same resolution stored together, EX satellite images

Displaying Multiband Rasters

§ Natural color (red, green, blue wavelengths)

§ False color (near infrared, red, blue)

DEM

Digital Elevation Models

Attribute Table

§ Stores attributes of map features
§ Spatial data layer
§ Special fields for spatial info

Standalone Table

§ Stores any tabular data
§ Not associated with spatial data

Sorting Records

Sorted ascending or descending; does not affect original data

Turning off fields in table

o Does not delete, just removes from display

Field Data Types

o Short and long for integers

o Float and Double for Decimals

o Text

o Date

Geometry Fields

special fields in attribute tables called Shape_Length and Shape_Area

Coded domains

provide lists of values to pick from; EX conifer or deciduous

Range Domains

specify the range of numeric values permitted

shapefiles

o area fields that must be manually created and updated
o Automatically updated fields in a geodatabase are called shape_area

SQL

Structured Query Language-- for relational databases

Query

o Built into layer which can temporarily remove unwanted features and can improve quality and speed of map display

Joins

o Temporary relationships between tables used by relationship DBMS

One to one cardinality

§ States to governors
§ Husbands to wives

One to many cardinality

§ States to cities
§ Districts to schools

Many to one cardinality

§ Cities to states
§ Schools to districts

Many to many cardinality

§ Students to classes
§ Stores to customers

Topology

o Spatial relationships between features

Logical consistency

o When topology match real world
Ex. Roads actually connect

Dangle

o Lines fail to connect

Coincident Boundary

o Shared edge that contains exactly the same x-y pairs for both adjacent polygons

Snapping

Ensures ends of roads or vertices of polygons match

Snap tolerance

distance of snapping points

Schema changes

o those that affect the structure of a table
o ex: adding/deleting fields, or modifying domains

Editing Changes

o Affect the properties of individual feature coordinates or attributes
o Not possible when there are unsaved schema changes

Feature templates

Quickly access construction tools and attributes for a layer; can have multiple

Annotation

Set of labels stored in a feature class

Reference Scale

o Maintains consistent placement relative to map features

Spatial operators

intersect, contains/within, proximity

Intersect

tests whether or not features touch

Contains/ Within

tests whether a feature is inside another

Proximity

tests whether features are within specified distance of another

zones

areas of raster/feature dataset that share the same integer value

contains operator

permits feature to lie on edge of containing feature

Completely contains operator

does not permit a shared boundary

Target layer

layer in spatial query from which features are selected

source layer

layer in spatial query that target features are compared to

Overlay

provides a way to split features so there is always a one to one correspondence

Extraction functions

Clip, Erase

§ Clip and erase can change lengths or areas of features on boundary

Clip

keeps features inside feature boundary

Erase

keeps features outside feature boundary

On the fly clipping

o Temporary clip applied to map layout
o Performed on many layers simultaneously

Sliver polygons

o Tiny polygons created during geoprocessing
o Result of slight differences in boundaries

Model Builder

o Way to string functions together to create work flow
o Useful for grouping sets of related functions for repeated use
o Created inside toolboxes
o Can be shared with others and converted to scripts

Spatial Interpolation

Computational procedure for estimating surface values for continuous variables at unsampled locations

Raster Calculator

Combines different rasters into one big raster

Neighborhood functions

mean, majority, variety

Zonal Functions

o Two input data – zone layer: defines boundaries of zone – Value layer: defines the value of the phenomena

Density Functions

o Count number of features within specified circle, divide by circle area to yield density value

Heatmap

Symbology draws point features as a dynamic, representative surface or relative density

Least Cost Path

Uses cost raster (slope) to quantify cost of travel and combines it with distance raster to determine the easiest route between points

Aspect

o Deepest downslope direction
o Determines direction of water flow over terrain surface

Shaded Relief Map

o Shadow effect produced by interaction of sun with topographic surface

Viewshed Analysis

o Region that is visible from a given vantage point in the terrain

Flow Direction

o Determined by comparing elevation data of a cell to its neighbors

Snapping

o Used to snap or align an extent during execution
o When output cell is same size as snap raster size, the cells in output raster are aligned with cells of snap raster

Resources

Data sets, web maps, geoprocessing services

Data sets

can be downloaded and stored locally

web maps

provide content that can also be used by mobile devices

Geoprocessing services

allow analysis to be performed on server side

Work flow

o Sequence of data management or analysis steps needed to complete task, allows less chance for errors

Metadata

Data about data; where it came from, how it should be used

CSDGM

content standard for digital geospatial metadata

lineage

where data came from and how it was processed, metadata related to data quality

feature layer

point, line, or polygon features and their attributes