GIS Data Primer Rich Gallacher, GISP GIS Coordinator Town of Manchester, CT
GIS Data is Extra Spatial
80% of all data has spatial component
The spatial component of GIS data makes
them more powerful
Can ask the “where” related questions
Spatial analysis can be done in minutes
instead of days
Key Concepts
GIS data represents geography (features of a specific location) that a computer can understand
Used to help make models for better managing those features
Graphically reveals the GIGO-sity of a dataset
Consist of a map component and a tabular element
Typically divided into two types; vector and raster
Have varying levels of accuracy, completeness and timeliness
Supported by standards
The Coordinate System Sandwich
If all the data in a GIS is in the same coordinate or geographic reference system then they all can be used together
What’s your vector, Victor?
Similar to CAD data
Represents linear features, i.e. points, lines & polygons
X Y coordinates that make up the feature stored in GIS
GIS uses XY coordinates to create the graphic representation and perform analysis
Gives us XY location (points), length (lines), perimeter and area (polygons)
Points Lines Polygons
Raster MonImagery, hot spot maps, climate maps, etc.
Uses an array of cells, or pixels, to represent real world objects
Continuous data such as elevation, slope or vegetation
Cell size determines the resolution of data – not horizontal accuracy!
Each cell contains attribute values such as RGB for imagery, avg temp for a climate map or avg slope, etc.
CRCOG 2009 3” Color Ortho’s Elevation Raster of Manchester
Other Data Terms You Might Hear
Geodatabase – ESRI’s de-facto data format
Shapefile – ESRI’s non-proprietary data format
Datum – a parameter of a data set’s coordinate system
Geo-referenced – data geographically reference and ready to be use by in a GIS
Topology – the spatial relationship between connecting or adjacent features
Orthoimagery – geo-referenced aerial imagery with distortions and errors removed
Digital Elevation Model (DEM) – raster elevation dataset used to create contours and perform surface analysis
LIDAR (light intensity detection and ranging) – lasers are shot from an airplane and capture surface elevation –used to create DEM’s
Not All Data Are Created Equal
Accuracy
Completeness
Timeliness
Update Frequency
Purpose
Source Map Scale
QA/QC & Metadata
Not a fun job in the GIS world but worth it
Investment in the data and in the GIS as
a whole
http://www.fgdc.gov/metadata/geospatial-
metadata-standards
You Are Not Alone!
Dozens of standards and data models are already developed
…free data, too!
Where to start…
FGDC - http://www.fgdc.gov/metadata/geospatial-metadata-standards
CGISC - http://www.ct.gov/GIS/cwp/view.asp?a=3034&q=404742
ArcGIS Resource Center - http://resources.arcgis.com/content/data-models
CT ECO - http://www.cteco.uconn.edu/
MAGIC - http://magic.lib.uconn.edu/
GIS Data TrendsMobile capture & editing devices, i.e. Android, iPad, Galaxy Tab, etc.
KML & Google Maps
3-D
Thanks for coming and happy
mapping!
Any questions?
Rich Gallacher, GISP
860-647-3062