Spatial Data: Elements, Levels and Types

Spatial Data: What GIS Uses

Bigfoot Sightings: Spatial Data

A GIS Provides the Ability to Analyze Disparate Data Sets Based on Location

Spatial and Attribute Data

Spatial data (where) specifies location

Attribute data (what) specifies what is at that location stored in a database table

A GIS will link spatial and attribute data for display or analysis

4 Types of Phenomena

Spatial Elements

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Points

Points occur at one location in space.Examples include houses, trees etc.Discrete or fixed: Occupies one space at

any time.Moving: Examples include, cars, fish, deerThey have no spatial dimension.

Lines

Occupy a single dimension.Examples include: roads, boundaries, and

networks.Do not have a width, but length can be

measured.

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Area

2-dimensional objectsLength and width can be measuredSurfaces, which include two types:Discrete, has a definite boundary ex: townsContinuous, has a changing boundary ex:

meandering river

Volume

3-dimensional.Examples include the volume of water in a

lake, air masses.Continuous data includes: elevation,

rainfall, ocean salinityMoving data includes: air masses, animal

herds, schools of fish

GIS Attempts to Describe All Features in Geometric Terms.

Points: surveyed locations, new construction, community resources

Lines: roads, transit routes

Areas: parcel maps, zip codes, census tracts

Data Types - 4 Types

nominal • no inherent ordering

• land use types, county names

• yes or no data

ordinal • inherent order

• road class; stream class

• hierarchy

• can be compared

interval•known distance between values

•no natural zero

•can be compared

ratio•natural zero

•ratios make sense (e.g. twice as much)

•income, age, rainfall

Data Types

GIS Links Spatial Data with Attribute Data for a Feature on a Map

The information is stored as ‘attributes’ of the graphically represented feature.

Example: A line that denotes a road shows its location. An attribute table stores all relevant information about this feature, which can be queried and displayed in a format based on the user’s needs

Roads Map

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Feature No. X,Y Pairs

1 3,5 5,52 5,5 8,53 8,5 9,54 6,9 5,4 5,7 5,6 5,55 5,5 4,4 4,16 0,5 3.2

Feature No.Road-Type Surface Width Lanes Name1 2 Asphalt 48 4 N. Main St.2 2 Asphalt 48 4 N. Main St.3 2 Asphalt 48 4 N. Main St.4 1 Concrete 60 4 Hwy. 425 1 Concrete 60 4 Hwy. 42

Feature List

Attribute Table

There are Two Ways to Acquire Spatial Data to Put Into a GIS

1. You purchase, or are given an existing data set2. You go out and collect the data yourself

Major GIS Data SourcesMapsDrawings (sketch or engineering)Aerial (or other) PhotographsSatellite Imagery/Digital Ortho PhotographyCAD data basesGovernment & commercial spatial (GIS) data basesGovernment & commercial attribute data basesPaper records and documents

Where do we get the data?

Purchase the data already processed and ready to use.

Purchase the data and then complete the processing.

Get original data in office or lab.Get original data in the field.

Existing Data

Purchase satellite images/ aerial photography already processed

Find public domain sources of images. Or share costs with data partners.

Purchase or download data and process in-house.

Existing Data

We may purchase or share an attribute data base (Excel spreadsheet, or Access database).

Must have a spatial component. Sometimes we must “clean” the data.

Data Collection

Compile data directly from air-photos.Digitize from existing paper mapsScan from existing mapsField data collection. Hand-held, mobile

and airborne GPS (Global Positioning Systems).

Creating your own data

Manual Digitizing Raster Scanning

Most GIS users still must create their own data or need to update it

Pre-processing and Conversion: usually required!

Maps and Drawings digitizing, or scanning

Aerial Photographs photogrametry/photo interpretation to

extract features digitizing or scanning to convert to digital

Satellite Imagery/ Digital Orthophotography

rectification and DEM (digital elevation model)

CAD Data Bases translator software (pre-existing or custom-

written) needed to convert to required GIS format

GIS Data Bases conversion between proprietary

standards (ARC/INFO, Intergraph, GDS, etc.)

Spatial Data Transfer Standard

Attribute Databases geocoding if micro data conversion between geographic units

Records and Documents OCR (optical character recognition)

scanning keyboarding then, same as attribute data bases

Representation of space elements...

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Computer Perception

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