Info Tech Exam 1.2

What is attribute data and what types of geospatial data have it?

What is attribute data and what types of geospatial data have it?

It provides characteristics about spatial data beyond location

What makes something spatial data?

if it references location for its basis

What are some reasons we need to use GIS’s?

GIS is easy to manipulate

good for large data points

easy to share

Uses of attribute data

to symbolize map features

select features

serve as variables for analysis

Rows

records

columns

attributes

single symbol

categories

quantified

the ways ArcMap assigns breaks to continuous data and why you might use them

So you can take out the data you don’t need

Makes data easier to manipulate

You can select data based on:

filter

query

interactive selection

Reasons to select features:

perform calculations on just selected features

highlight for visualization

create dataset from selected data

Once you have a selection you can:

add

remove

select from

switch

clear your selection

(TYPE=”UH”) OR (TYPE=”LP”)

Select all with that are either type UH or type LP

(TYPE=”UH”) AND (AGE<30)

select all that are both type UH and less than 30 years old

Interactive select

click on the selection you want

Select by location

select by intersection, distance from, touching…

Raster

features depicted by contents of grid cells

pixelated up close

better for land cover

good for large datasets

worse for having a loss of small info

Vector

features defined by coordinate pairs

high resolution up close

better for buildings and roads

does not lose clarity up close

larger data set

Files in a shapefile

shapename.shp

shapename.dbf

shapename.shx

common files extension for raster

.tif

.bmp

Common file extension for vector

.shp

Nominal

think names

no numeric meaning or relative ranking

may use numeric codes

Ordinal

labels or categories

but ranking is meaningful

difference between categories might not be consistent

1rst, 2nd, 3rd,…

very good, moderate, poor

Interval

numerical values

zero is not absolute

ratios not always meaningful

time and temperature

pH

Ratio

zero is absolute

zero doesn’t change with units

ratios meaningful

Integer

whole number

short/long

float

has a decimal

single/double

DEM

digital elevation model

DRG

Digital raster graphic

Components of a map

North Arrow

Scale Bar

Bounding Box

Legend

Title

All projections

distort the earth

Geographic coordinate system

angular units (not distance) (degrees, minutes, seconds)

doesn’t involve a projection

latitude, longitude, parallel, meridian

Projection coordinate system

projection of the earth onto a plane

cartesian coordinates (x,y)

distance units (meters, feet,…)

mathematically defined

Angular

degrees, minutes, seconds

Cartesian

(x,y)

Common coordinate systems:

geographic

state plane

utm

Datum

represents assumptions about the shape of the earth

Why is UTM accurate at smaller scales?

Split into zones - zones matter

It minimizes distortion by doing this

Why do states use different projections for their state plane coordinate systems?

To minimize error

states may be broken up into zones

choose different projections based on shape

Projections

there will always be distortion

UTM scale

good at small scale

Geographic scale

good at big picture

State Plan scale

good at state scale

Where to find Coordinate system

in metadata

Dataframe

complete maps to themselves

Layers

different sets of data and displayed within the data frame

projected into the coordinate system of the dataframe

Layer coordinate systems

can be different but it is better if they are the same if you are calculating area and/or distance

When projection isn’t defined

you just have to figure it out

can still use data

How GPS receivers determine their location

read the differences in times sent by different satellites to triangulate its location.

3 components of GPS

satellites

control (monitor, orbits and clock)

and GPS receiver

common sources of GPS error

Ionospheric Delay

Clock Errors

Multipath Error

WAAS

keeps track of error and lets your GPS unit know

corrects clock error

Differential correction

using a base station with known location to test error

used to correct all error types

How many satellites do you need to get your position in 3d?

4

Accuracy

closeness of a measured value to a standard or known value

measure of bias

how close the test is to the true value

Precision

measure of exactness

how close the tests are to each other

How to measure area in arcmap

In attribute table, right click then calculate geometry

Standard Deviation

measure of the distribution of data

lower values means they are closer together

doesn’t use a true value

measure of preciseness

Root Mean Squared Error (RMSE)

uses difference from true value rather than just the mean

lower means closer to true value

How RMSE is calculated

(Observed- actual value) squared

Add together and divide by n – average

Take square root

Bias

Metric related to the systematic accuracy of the data

Not just random error