Copyright © 2006 by Maribeth H. Price 1-1 How does GIS work? Data storage The ArcGIS Interface

Copyright © 2006 by Maribeth H. Price

1-1

How does GIS work?

Data storage

The ArcGIS Interface


1-2

Vector model

Vertices

Polygon

Points

Nodes

Line

X

Y

Features are stored as a series of x-y coordinates in a rectangular coordinate system.

Many different coordinate systems may be used.


1-3

Features linked to data

Each feature is linked to an entry in a data table containing information about the feature.


1-4

Advantages of vectors

• Precise location of features

• Storing many attributes

• Flexible for cartography

• Compact storage of information

• Ideally suited for certain types of analysis, especially areas, lengths, connections


1-5

The raster data model

Rows

ColumnsX, Y location

Raster data fileN rows by M columns

X, Y location

Georeferenced to earth’s surface


1-6

GIS data models

Vector model Raster model

Digital Raster Graphic

Converting Vector to Raster Data is Easy


1-10

Types of raster data

Discrete raster: land use

Continuous raster: DEM

Continuous raster: image

Discrete raster: roads

Some Common Image Formats

• JPG – Used for most digital photos but “lossy.”

• GIF – Best for line drawings. 256 colors maximum. No loss

• TIF – Standard in many technical applications. No loss

• PNG – Lossless image format

• RAW – Data as captured by digital camera


1-12

Continuous data

• Raster is the best way to store continuously changing values such as elevation

• Analysis faster and more flexible than vectors for many applications

• Some analysis only possible using rasters


1-13

Raster analysis functions

Density

Least cost path

Distance Interpolation

ViewshedBuffers


1-14

Impact of resolution

• Storage space increases by the square of the resolution

• Portraying large areas at high precision is problematic

90m resolution

10m resolution


1-15

Storage of attributes

• Roads may have other attributes: ownership, speed limit, number of lanes, etc.

• Would need a new raster for each attribute

• Only numeric attributes may be storedRaster contains 1 value

indicating a single attribute—road type for example


1-16

The raster data model

Rows

ColumnsX, Y location

Raster data fileN rows by M columns

X, Y location

Georeferenced to earth’s surface


1-17


1-18

ModelBuilder• Create models built from sequences of tools• Store processing steps for later reference• Execute models repeatedly with different inputs• Share models with others


1-19

Moonlight BayBasin.shp

Discard out-of-boundaryspot elevations

Export todelimited text

Extract spotelevations every 50’ for 11 input datasets

Merge 11datasets

bh_c.shpContour2-

point_bhc.shp

Township2-Foot Contours

THE RIDGES SANCTUARYWATERSHED STUDY - 2006-2007

Geospatial Analysis - Summary Flow Diagram Revision Date: 10 September, 2007 By: Mike Stiefvater

Boundary Of AreaTo Be Modeled

WS0607-Boundary.shp

Final Spot ElevationsIn x,y,c Format

Input01.txt

Thinned And Combined Township

Spot Elevations

Hydrologic modeling furnished by Door County

Soil and Water Conservation Department

Document Locationof Known Outlets

WS0607-outlet4model.shp

Calculated Subwatershed Boundaries

South Outlet*Basin.shp

Calculated Flow Paths

Flow path.shp

“Thinned” Elevation Data

Contour2-point_all.shp

FinalSpot Elevations

Contour2-point_clip.shp

WS0607-Culvert.shp

Hwy 57Basin.shp

Mud Lake Basins.shp

Analytical Operation/GeoprocessingTool

Dataset

* aka “Hidden Brook Subwatershed”

Documents

Copyright © 2006 by Maribeth H. Price 1-1 How does GIS work? Data storage The ArcGIS Interface