Data Acquisition

Lecture 8

Data SourcesData Sources

Data TransferGetting data from the internet and importing

Data CollectionOne of the most expensive GIS activities

Many diverse sourcesRaster based satellite dataAerial picturesSurveying

Data TransferGetting data from the internet and importing

Data CollectionOne of the most expensive GIS activities

Many diverse sourcesRaster based satellite dataAerial picturesSurveying

Data CollectionData Collection

Data Capture (Direct Collection)Primary (Direct Measurement)Secondary (Indirect Measurement)

Data Capture (Direct Collection)Primary (Direct Measurement)Secondary (Indirect Measurement)

Raster Vector

1o

Digital remote sensing images

Digital aerial photographs

GPS Measurement

s

Survey Measurement

s

2o

Scanned Maps

DEMs from Maps(Digital Elevation

Models)

Topographic Surveys

Toponymy data sets from atlases

Table Digitizing

1o Raster1o Raster

Capture specifically for GIS useRemote sensing - Raster Data

E.g. - SPOT & IKONOS satellites and aerial photography

Passive & Active sensorsPlatform

Airplane, satelliteSensor

Device that records spatial dataCamera - B & W (Panchromatic)Infrared Sensor - Hyperspectral imagery

Capture specifically for GIS useRemote sensing - Raster Data

E.g. - SPOT & IKONOS satellites and aerial photography

Passive & Active sensorsPlatform

Airplane, satelliteSensor

Device that records spatial dataCamera - B & W (Panchromatic)Infrared Sensor - Hyperspectral imagery

ResolutionResolution

Resolution of Raster data is a key considerationSpatial

What size object can be resolvedWhat size is a pixel

SpectralWhat part of the EM spectrum is being measured

TemporalHow often is the data being updated

Resolution of Raster data is a key considerationSpatial

What size object can be resolvedWhat size is a pixel

SpectralWhat part of the EM spectrum is being measured

TemporalHow often is the data being updated

Spatial-Temporal Characteristics of Remote Sensing Systems

"Spatial and temporal characteristics of commonly used remote sensing systems andtheir sensors" From:  Geographic Information Systems and Science, 2nd ed.Paul Longley, Michael Goodchild, David Maguire, and David Rhind.  Originally From:Jenson, J.R. and Cowen, D.C.  1999 'Remote Sensing of urban/suburban infrastructureand socioeconomic attributes' PERS, 65, 611-622.

1o Vector1o Vector

Surveying Location of objects determined by angle and distance measurements from known locations

Uses expensive field equipment and crewsMost accurate method for large scale, small areas

GPSCollection of satellites used to fix locations on earth’s surface

Increased accessibility

Surveying Location of objects determined by angle and distance measurements from known locations

Uses expensive field equipment and crewsMost accurate method for large scale, small areas

GPSCollection of satellites used to fix locations on earth’s surface

Increased accessibility

2o Geographic Data Capture

2o Geographic Data Capture

Data collected for other purposes can be converted for use in GIS

Raster conversionsScanning of maps, aerial photographs, documents, etc

Important scanning parameters are spatial and spectral resolution

Digitizing, Batch VectorizationCommon human errors in digitizing

Overshoot, undershoot, dangling segment, sliver polygon

Automated remedies to digitizing errors are not perfect

Data collected for other purposes can be converted for use in GIS

Raster conversionsScanning of maps, aerial photographs, documents, etc

Important scanning parameters are spatial and spectral resolution

Digitizing, Batch VectorizationCommon human errors in digitizing

Overshoot, undershoot, dangling segment, sliver polygon

Automated remedies to digitizing errors are not perfect

Quality StandardsQuality StandardsMetadata

Information about the dataWho Collected the dataHow was it collectedWhat datum was usedWhat projection was usedWhat is the precision of the dataWhat type of data is itWhen was the data last updated

There are standards established for different types of data and the metadata.

Metadata should be available for the data to be reliable.

Metadata should be available either for each data file, or a general metadata file will be available for a group of files.

MetadataInformation about the data

Who Collected the dataHow was it collectedWhat datum was usedWhat projection was usedWhat is the precision of the dataWhat type of data is itWhen was the data last updated

There are standards established for different types of data and the metadata.

Metadata should be available for the data to be reliable.

Metadata should be available either for each data file, or a general metadata file will be available for a group of files.

AccuracyAccuracyThe degree to which information on a map or a digital database matches true or accepted values.

Accuracy is an issue pertaining to the quality of data and the number of errors contained in a dataset or map.

The level of accuracy required for particular applications varies greatly.

Highly accurate data can be very difficult and costly to produce and compile.

The degree to which information on a map or a digital database matches true or accepted values.

Accuracy is an issue pertaining to the quality of data and the number of errors contained in a dataset or map.

The level of accuracy required for particular applications varies greatly.

Highly accurate data can be very difficult and costly to produce and compile.

http://www.colorado.edu/geography/gcraft/notes/error/error_f.html

PrecisionPrecision

The level of measurement and exactness of description in a GIS database.

Precise locational data may measure position to a fraction of a unit.It is important to realize that precise data - no matter how carefully measured - may be inaccurate.

Surveyors may make mistakes or data may be entered into the database incorrectly.

The level of measurement and exactness of description in a GIS database.

Precise locational data may measure position to a fraction of a unit.It is important to realize that precise data - no matter how carefully measured - may be inaccurate.

Surveyors may make mistakes or data may be entered into the database incorrectly.

The level of precision required for particular applications varies greatly.Engineering projects such as road and utility construction require very precise information measured to the millimeter.

Demographic analyses of marketing or electoral trends can often make due with less, say to the closest zip code or precinct boundary.

Highly precise data can be very difficult and costly to collect.

The level of precision required for particular applications varies greatly.Engineering projects such as road and utility construction require very precise information measured to the millimeter.

Demographic analyses of marketing or electoral trends can often make due with less, say to the closest zip code or precinct boundary.

Highly precise data can be very difficult and costly to collect.

http://www.colorado.edu/geography/gcraft/notes/error/error_f.html

Error in dataError in data

Positional Accuracy and PrecisionHorizontal and VerticalScale

Attribute Accuracy and PrecisionNon-spatial information linked to a locationE.g. Age, gender, income of a person at a particular address

Positional Accuracy and PrecisionHorizontal and VerticalScale

Attribute Accuracy and PrecisionNon-spatial information linked to a locationE.g. Age, gender, income of a person at a particular address

Conceptual Accuracy and PrecisionAbstraction and classification of real-world phenomena.

The user determines what amount of information is used and how it is classified into appropriate categories.Rivers, streams, tributariesElectrical utilities infrastructure

Voltage, line size, line type

Logical Accuracy and PrecisionInformation in a database can be employed illogically.

Information in a GIS database must be used and compared carefully if it is to yield useful results.

Conceptual Accuracy and PrecisionAbstraction and classification of real-world phenomena.

The user determines what amount of information is used and how it is classified into appropriate categories.Rivers, streams, tributariesElectrical utilities infrastructure

Voltage, line size, line type

Logical Accuracy and PrecisionInformation in a database can be employed illogically.

Information in a GIS database must be used and compared carefully if it is to yield useful results.

http://www.colorado.edu/geography/gcraft/notes/error/error_f.html

Canned Data vs External Data

Canned Data vs External Data

Canned Datadata that has been pre-screened and tested to work in a particular application.For example: the data sets in Mapping Our World and Getting to Know ArcGIS.

External DataData in the form that is made available by the supplier.For example: the data sets from SANDAG or SanGIS.

The data may not be in the same datum, projection etc.

The data may need to be manipulated before it can be projected correctly.

Canned Datadata that has been pre-screened and tested to work in a particular application.For example: the data sets in Mapping Our World and Getting to Know ArcGIS.

External DataData in the form that is made available by the supplier.For example: the data sets from SANDAG or SanGIS.

The data may not be in the same datum, projection etc.

The data may need to be manipulated before it can be projected correctly.

Downloading from Web Sources

Downloading from Web Sources

Use reliable sitesGovernment or Education Sites

Reliability of dataCheck the metadata for:

Source of the dataAccuracy and Precision of the dataDate of data collection and revision

Format of the dataCheck the metadata for:

DatumProjection

Use reliable sitesGovernment or Education Sites

Reliability of dataCheck the metadata for:

Source of the dataAccuracy and Precision of the dataDate of data collection and revision

Format of the dataCheck the metadata for:

DatumProjection