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

Which is easier to make hard decisions with?

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

Great pair…says the Bear!

GraphicTable

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

GIS Data Types & the Big Picture

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

RichG@manchesterct.gov

860-647-3062