Geographic Information Systems. Introduction to Data and Data Sources

Transcription

1 Geographic Information Systems Introduction to Data and Data Sources Presented by John Showler, NJDA-SSCC NJ SCD GIS Training Session December 10, 209 The Objectives of this session are 3-fold: 1. Introduce the various kinds of data 2. Examine key characteristics of these data 3. Discuss various sources for procuring data 1

2 Kinds of Data used in GIS Spatial data- Points, lines, polygons Tabular (tables) Attribute of the spatial layer Stand-alone tables linked to layers Linked tables from outside the GIS environment Raster TIFF, JPEG, MrSid, Natural color, Color IR Kinds of Data used in GIS continued CAD (computer aided design) Elevation Data Triangular Irregular Networks (TIN) Digital Elevation Model (DEM) Digital Terrain Model (DTM) CoGo (coordinate geometer) entering bearings and distances to define polygons) 2

3 Spatial Data Points Survey elevations Lines HEC RAS sections Polygons channel Perimeter Point Data Identifies singular data- Basin outlets Surveyed elevation points Manholes Location of photos taken Location of SCD offices Data represented by single X-Y coordinate + attribute information(name, ID # etc) 3

4 Lines Can be single lines or poly-lines (looks like a polygon, but does not have a sense of topology that is, what is next to it). Consists of a minimum of 2 points (beginning and ending) and a vector or ARC between them Yes, that s why its called ArcView or ArcInfo or ArcMap or Arc..whatever Point Spatial and Attribute Data FSCD Basin Locations in Wreck Pond Watershed 4

5 Polygon Attribute Data Poly Line Attribute Data 5

6 Arc Attributes Attribute Tables. Tabular Data All spatial data has tabular data behind it. This is called, attribute data table. Each record in the attribute table refers to a single graphical item (one, point, one line, one polygon) in a data layer (roads, lakes, wells, soils, land use etc) Stand-Alone Tables. GIS can include stand-alone text tables (nonspatial) that can be linked to a spatial data layer to expand the information available for analysis. These can be dbase (dbf), CSV, TXT or XLS tables. All can be linked to the spatial attribute table. 6

7 Attribute Record Example. Each highlighted record corresponds to the blue-outlined (selected) soil/landuse polygons. The record to spatial entity is a one to one link. Sheet1$ is an imported stand alone Excel table that can be linked to the CN data layer to add information to each record (CN polygon) in the spatial data layer 7

8 Raster Data (images) Raster data refers to aerial image and digital elevation data. Aerial Image data is geo-referenced. That is, the photo, which has no information behind it like a normal data layer, is referenced to the map s coordinate system so images will line up with regular data such as roads, streams, lakes etc. The only information in a raster image is the color value of the pixel. Even this can be exploited. You can make images black and white for example, to emphasize spatial data this is in color Raster Image of Old Mill Pond Left: Color IR. Right: Grayscale. RAS cross sections modified to enhance contrast 8

9 Color IR- Low Resolution Healthy vegetation shows as bright red. Also distinguish living/dead vegetation Natural Color Higher Resolution. More detail, better measurments. Harder to evaluate health of vegetation Computer Aided Design (CAD) CAD files (dxf) can be read directly by GIS as a series of layers. GIS can filter (turn on or off) layers to focus on desired data such as perimeters of areas (i.e. footprint of a site). 9

10 Elevation Data Elevation data is displayed as a grid of cells. Each cell has one elevation data point. The size of the cell is given in feet or meters. Small cell size = fine resolution (i.e. 1 foot or 1 meter on a side) Large cell size = course resolution (i.e. 10 meter on a side). Large cells draw faster and are ok for large areas where small changes in elevation don t matter (i.e. watershed) Small cells draw slower and are needed for showing subtle changes in elevation (i.e. HEC RAS modeling). Digital Elevation Model (DEM) Grid. One value per cell Triangular Irregular Network (TIN). Derived from DEM s. Can be augmented with other data 10

11 CoGo Coordinate Geometry Not a data type per se. A method of using existing survey data from paper maps or deeds. A utility in ArcInfo (big bucks) that allows the user to input bearing and distance from one survey point to the next and create a GIS data layer (poly line or polygon). We probably wont use or need it, but you should be aware that it exists. A great tool if you do that kind of work, and have the $$ for it. Coordinate Systems and Projections The Earth is not flat. It is also not round. VERY IMPORTANT!!!! It tends to be an ellipse or a spheroid In order to measure things on the flat surface of the ground, which is not really flat, you need to have a way of finding locations of things and accounting for the curvature of the earth. Cartography vis a vis GIS uses complex formulas to convert curved distances to linear so that we can use the information. 11

12 What is a Coordinate System? A coordinate system is a measured grid overlaid so that we can measure distances and areas. GIS uses many, many kinds of systems Geographic latitude and longitude Projected systems UTM, State Plane State Plane every state has its own This is NJ s: Units of feet or meters is common. NJ uses feet. We also use the NAD 83 as our datum 12

13 North American Datum 1927 vs The State of NJ uses NAD 83 The good news is Arc GIS will convert any data layer to a common projection on the fly as you add it to the map table of contents (data window). The top most data layer sets the coordinate system used by GIS to adjust all subsequent layers. You can also set the coordinate system manually, or turn off projection on the fly altogether. For simplicity, just make sure your data is in NAD 83 SP Feet for NJ and you will be good to go. 13

14 How do you know what you have in your data? Metadata! (data about data ) Metadata is information that documents all aspects of the data layer you are using. It must be prepared by the person who develops the data. Some of it may be auto generated such as projection, but the description of table fields, levels of accuracy etc. must be added manually. Otherwise, all you have is a pretty picture. Example Metadata 14

15 Example Metadata Example Metadata 15

16 Example Metadata Uses for GIS (data) Aerial measurements (limits of disturbance) Location of natural resources and measurements (stream length for Tc calculations) Computations Curve numbers, rainfall depth Photo interpretation changes in a project over time Cuts and fills Modeling of runoff and stream flow, view sheds General purpose spying High Res spying Only limited by your imagination. And the law. 16

17 Data Sources 10 years ago, the only source was NJDEP and you had to know somebody. Data was distributed on CD. Now, anybody (like, anybody) can go online and get data for any place in the world. Google is your friend. Here are some sources commonly used in NJ. GIS Data Sources in / for NJ: (NJ NGIN) ( a personal favorite) (USDA soil data mart) (USGS national data center) NJ Dept. of Agriculture Most of what DEP has, certain preserved farmland layers. Not on line. (Pinelands) (NJ Highlands) NJ DOT NJ Office of Smart Growth (state planning) NJ Parcel (tax map data) not downloadable yet. NJDA has some. Will be forthcoming from the State. Check local county GIS offices. 17

18 Data Sources Make your own Digitize right on the screen (heads-up digitizing) Construct a table of X-Y coordinates of things GPS points Edit other data split polygons of soils, towns, etc. Create look up tables to join to existing data layer attribute tables 18