CE 250 - Introduction to Surveying and Geographic Information Systems eLearning Version Donald J. Leone, Ph.D., P.E. Lecture 2

Introduction Spatial Data – How is it described? Spatial Data – Main sources. More on Rasters and Vectors Spatial Data Models Two new Spatial Data Entities Numerical Characteristics of Attributes.

Definition Spatial Data: Information about the geographic position of features Geographic Position – Usually an x,y coordinate pair in two dimensional space

GIS Model Building Model – “Simplified “ view of the “real” world. Computer generated representation. Constructed using spatial data.

Nature of Spatial Data Data vs. Information - Metadata Primary data – first hand knowledge Secondary data – collected by someone else Spatial data types Temporal – when, where, etc. (Metadata) Thematic – describes real world feature (Attributes) Spatial – location of feature (x,y)

Traditional Maps Influence how we characterize spatial data. Purpose Scale Select features Adopt a map projection Select a spatial reverencing system Annotate

Scale Definition – Indicates how much smaller than reality a map is. Ratio – Distance on a map to the distance on the ground. 1:5000 – 1 cm on map = 5000 cm on ground or 50 m Graphical 1 cm 0m 50m 100m 150m

Scale – Continued “small scale maps” Cover large areas Large ratio’s – 1:2,000,000 “small scale maps” Cover large areas Small ratio’s – 1:25,000 “large scale maps” Cover small areas

Scale Related Generalization The level of detail shown is directly related to scale

Map Projections Transfer spherical earth to flat surface. Many types of projections used world-wide. There will always be some distortion generated in the projection process.

Projection Techniques Cylindrical Projection

Projection Techniques Azimuthal Projection

Projection Techniques Conic Projection

Spatial Referencing Geographic Coordinate Systems (3D) Rectangular Coordinate Systems (2D) Non Coordinate Systems, i.e. zip codes

Geographic Coordinate System Latitude and Longitude Parallels - Meridians

Geographic Coordinate System Latitude and Longitude Angles Prime Meridian 00 Longitude Latitude – North Longitude - West Equator 00 Latitude

Latitude – Longitude Calculation

Little Grey Cells Quiz Large scale maps cover large areas. T or F Why are projections needed? Why do you think the prime meridian goes through Greenwich, England?

Rectangular Coordinates (2D)

Universal Transverse Mercator (UTM)

The State Plane Coordinate System - SPCS Used primarily for engineering applications Arbitrary origin - An arbitrary number of feet south and west of the most southwesterly point on the map. Eastings (x) and northings (y) all come out positive. Advantage: Accuracy Disadvantage: Lack of universality, as each state has it’s own coordinate system.

Break!

Other Sources of Spatial Data Census Data – TIGER Files Topolocally Integrated Geographic Encoding Referencing

Other Sources of Spatial Data Aerial Photographs Increased Altitude Produces smaller scale maps Distortion toward the edges

University of Hartford Aerial Photo Sports Center HJG Center UT Hall

Other Sources of Spatial Data Satellite Images LANDSAT Image Morro Bay, CA

Other Sources of Spatial Data Surveying The Global Position System – GPS www.trimble.com

GIS Software Spatial Data Modeling Real World Spatial data – Map, etc. Raster Vector GIS Software Spatial Data Structure Computer

Raster Data Structure Feature Model Cell Values File Structure

Vector Data Structure Line or Arc Number Node or Point Number

Vector Data Structure - TOPOLGY Topology - “The property that describes adjacency and connectivity of features” Newer structure for Vector data - Topological Arcs File - added to previous data. Used to build polygons that touch each other exactly.

Vector Data Structure - TOPOLGY

Two New Spatial Entities “Old” three – Points, Lines, Polygons Add two more – Surfaces Networks

Surfaces Snowdonia National Park, Wales

Surfaces Snowdonia National Park, Wales

Raster Digital Terrain Models – DTM Digital Elevation Model (DEM) - Njolomole, Malawi

Vector DTM’s Triangular Irregular Network - TIN

TINS - Surface Significant Points Eliminate points that are close together and similar – Cuts down on storage requirements. Those points that cannot be interpolated from their neighbors – Surface Significant. Surface Significant points are used as vertices in the TIN

Modeling Networks Network – “A set of interconnected line features through which material, goods and people are transported. or Along which communication of information is achieved.”

Networks Impedance – The cost associated with traversing a network link, making a turn, or stopping.

Raster and Vector Data Models

Raster and Vector Data Models

Thematic Characteristics of Spatial Data aka - Attributes Gives information about the feature. Allow certain GIS operations – like “Query”. Scale of measurement of the attributes is important.

Scales of Measurement of the Attributes Nominal: Assign a label or class to a feature, e.g. 1 is a well, 2 is a catch basin. Ordinal: Have a rank assigned to them e.g. 1 is light, 2 moderate, 3 heavy. Interval: Values measured on relative scale e.g. elevations measured from some datum. Ratio: Values measured on an absolute scale e.g. coordinates or total precipitation.

How to Construct a Spatial Data Model Purpose Scale Select features Adopt a map projection Select a spatial reverencing system Annotate

What’s Next Attribute Data Management. Data Input and Editing.