GSP 270 Digitizing with an Introduction to Uncertainty and Metadata Reading Assignment: Bolstad Chapter 4

Where does data come from? Surveying Existing Hardcopy Maps Aerial photography & satellite imagery GPS Field surveys, often in MS-Excel Direct to Internet Twitter Data Sources. Where do we get the data that we use in our GIS? Internet -> Often times finding the data you need is just a matter of conducting a good old fashioned Google search . -> Complied list of about 50 sources -> document on Moodle. Very small subset. Lab portion of Moodle -> References -> Online_Geospatial_Data_Sources_v3.pdf Lab 5 ->Tabular data (spatial data -> adding x,y geocoding, aspatial data through joins and relates). Global Positioning System -> Many times, getting the data you need is a matter of taking a GPS unit out in the field. Can record point data. Record linear features and polygon features by turning it on walking around say, a lake. Sometimes we use directly. Also extract features from aerial photos and satellite imagery using a combination of manual and automated techniques. Nearly all geographic information recorded prior to 1960 was recorded in hardcopy form. Prior to widespread adoption of GIS (late 80’s), this was still the most common storage medium for spatial data. Now of course everything is digital, but still a wealth of geographic information that exists in hardcopy maps -> can extract that information through the digitizing process (learn about today).

Geodesy The science of measuring the shape of the Earth, and map projections, the transformation of coordinate locations from the Earth’s curved surface onto flat maps. NOAA NOAA NOAA

Landsat 8 Longest continuous satellite data set Entire earth, twice a month, at 30 meters

GPS ~20 meter to <1 meter accuracy $100 to $5000 Trimble Garmin

Digitizing Digitizing: The process of converting features on a map or image into digital vector data. Basic Methods Manual digitizing (tracing!) Scan digitizing That is what digitizing is all about. Not going to focus on scan digitizing. Can be as simple as putting a map on the flat bed scanner you have at home, bringing into your GIS as an image. Also have scanners that can extract features, like roads, from a map and convert them to vector.

Digitizing Manual Digitizing: Human guided coordinate capture from a map or image source (tracing). Heads-up Digitizing (On-screen) Manually digitizing on a computer screen using a digital map or image as a backdrop. Raster  Vector Hardcopy Digitizing Manually digitizing on a digitizing tablet using a hardcopy map or image. Hardcopy  Vector Two types of manual digitizing techniques. Those tablets in the back of the SA-Lab.

Hard Copy Digitizing Digitizing Digitizing Tablet Puck Process is a little bit different (concept is the same…tracing over features of interest to you).

Map Scale Map Scale: The relationship between distance on the map and distance on the ground. 1/24,000 or 1:24,000 1/250,000 or 1:250,000 1 unit on map equals 24,000 of same unit on the ground. 1 unit on map equals 250,000 of same unit on the ground. Segue into today’s topic…Map scale -- The relationship between distance on the map and distance on the ground. Scale can be reported using a scalebar. Often time reported as a representative fraction, as you see here…. Can be expressed using either a division sign or a colon Means the same thing. 1 unit measured on the map equals 24,000 1 inch on map, 24,000 inches in the real world, or 1cm =24,000 cm in the real world. Over here… 1/250,000 Which is a larger scale map? Left -> Why? Things appear larger. Model train that with a scale of 1:1, how big is it? -> Lifesize. Train that is 1:5,000 -> much smaller. Same principal with maps. Map with 1:1 scale. Things would appear lifesize. Don’t see a whole lot of maps that are 1:1, won’t cover much area. Or if it did, the paper would have to be huge! 1 divided by 24,000 is a larger number than 1/250,000 1/24,000 larger fraction than 1/250,000? Large scale map, objects will appear larger. You’re zoomed in more. Small scale map you’re zoomed out further. Objects will appear smaller. Large scale map will show more detail Small scale map will cover a larger area. Gorham & Westbrook are in Maine. US map 1:1,000,0000 A typical scale for a terrestrial globe is roughly 1:40 million Representative fraction, ratio, scale bar, word statement. ------------------------------------------------------------------------------------------------------------------------------------ What is map scale…heard it a lot. Scale changed. Scale on this map is 1 to 24,000 Can be expressed as a fraction or as a ratio . Scale bars. http://egsc.usgs.gov/isb/pubs/factsheets/fs01502.html Scale of your map is not fixed in a GIS. Small scale map things appear small. 1 unit distance map = 24 of the same unit in the real world. A large scale map refers to one which shows greater detail because the representative fraction (e.g. 1/25,000) is a larger fraction than a small scale map which would have an RF of 1/250,000 to 1/7,500,000 Maps are often known as large scale or small scale. A large scale map refers to one which shows greater detail because the representative fraction (e.g. 1/25,000) is a larger fraction than a small scale map which would have an RF of 1/250,000 to 1/7,500,000. Large scale maps will have a RF of 1:50,000 or greater (i.e. 1:10,000). Those between 1:50,000 to 1:250,000 are maps with an intermediate scale. Maps of the world which fit on two 8 1/2 by 11 inch pages are very small scale, about 1 to 100 million. Map over on the left…zoomed in more. 1 inch measured on the map represents a shorter distance. Larger Scale Map Objects are larger (more detail) Area Shown: 1 square mile Smaller Scale Map Objects are smaller (less detail) Area Shown: 107 square miles

Nice things about a GIS….scale is not fixed.

1 inch = 1,200 inches (100ft) 1 mile = 63 360 inches

Digitizing Errors Undershoots Overshoots Digitizing Positional errors are inevitable when data are manually digitized.

Set a fuzzy tolerance (snapping tolerance) Digitizing Set a fuzzy tolerance (snapping tolerance) Used to reduce undershoots and overshoots. The minimum tolerated distance between nodes, lines and/or vertices.

Digitizing Characteristics of manual digitization that may negatively affect positional quality of spatial data. Map scale (not a problem for heads-up) Digitizing from small scale maps will introduce larger positional errors. Device precision The minimum distance below which points cannot be effectively digitized as separate locations. The abilities and attitudes of the person digitizing. Attention to detail Ability to concentrate Steadiness of hand (too much coffee) No fixed scale in GIS. See page 138 in Bolstad -> use graphic! As listed in Bolstad, here are… Heads up digitizing, DPI of your mouse. Hard copy depeend

Digitizing Page 138 in Bolstad -> use graphic!

Digitizing Scale – 1:100,000 Scale – 1:5,000 Map Scale Example – Grizzly Lake Trinity Alps Wilderness

Metadata Data about the data What is really critical? Source of the data (URL) Contact for additional information Date of acquisition Next most critical? Collection/processing protocol How the data was collected and/or processed What was the original purpose? Approximate uncertainty Make sure all data has the source, contact, and date of acquisition

Standards Organizations FGDC: Federal Geographic Data Committee New federal geospatial platform: www.geoplatform.gov ISO: International Standard Organizations Many others within specific fields of interest

Metadata Standards FGDC: ISO 19115:2003 http://www.fgdc.gov/standards/projects/FGDC-standards-projects/fgdc-endorsed-standards ISO 19115:2003 http://www.iso.org/iso/catalogue_detail.htm?csnumber=26020 Have to pay for it from ISO