What Do You See? FOR 274: Forest Measurements and Inventory. Area Determination: Frequency and Cover

Transcription

1 What Do You See? Message of the Day: Many options exist to determine the size, area, or extent of a feature on a landscape FOR 274: Forest Measurements and Inventory Lecture 7: Measures of Land Area Frequency and Cover Area Measures Reading Maps Area Determination: Frequency and Cover Frequency: The rate (or chance) of finding a given feature when a particular sample is located in an area Cover: The horizontal extent of trees, shrubs, grass, etc when viewed from above Source: Bonham 1989 Photo: A Hudak (USFS) 1

2 Area Determination: A Simple Closed Transverse Purpose: Locate approximate boundaries of a tract and determine the enclosed area Most surveys involve 3 or 4 people: - 2 people chain horizontal distances - 1 person establishes compass lines and records values Area Determination: A Simple Closed Transverse Start at most reliable property corner: At end of transverse add up all angles Sum should equal (n-2) x 180 (n = sides of tract) If you have one record each corner with a GPS unit Area Determination: An Example of Methods So how can we measure the forest cover in this image? 2

3 Area Determination: Dot Grids Each square = 8 ac If 40 dots per big square then each dot ~ 0.2 acres Points: May use denser grids to increase precision or when the region is small Should use average of several random orientations Area Determination: Line Intercept Total Length = 140 inches Assume % of area of each land cover class (forest, clearcut, ag, etc) = proportion of line intercepting that class e.g., 14 inches of clearcut = 14/140 = 10% of the area Area Determination: Via a GIS If map scale and projection is known Use ARC to create a polygon and basic functions to calculate area of each polygon 3

4 Map Reading: A Brief History of Maps 8 th Century BC World map Land is surrounded by ocean and divided by the Euphrates River Beyond ocean are 7 more bits of land hinting knowledge of more land Map Reading: A Brief History of Maps An Early Map of Egypt Map Reading: A Brief History of Maps 1744 Map of France: Triangulation surveys by Jacques Philippe Maraldi and Cesar Francois Cassini de Thury This survey took three generations of the Cassini family to complete 4

5 Map Reading: A Brief History of Maps The Rise of Digital Data: Accuracy and detail have continued to improve with digital age Many maps were developed from terrestrial perspective Today aerial photography and satellite imagery have greatly enhanced our quality of maps. Map Reading: A Brief History of Maps The Rise of Digital Data: Geographic Information Systems (GIS) have made mapping technology available to any company Google Earth and Yahoo! Maps have made this technology digitally available For Foresters, there are many options available for mapping. Map Reading: Important Points Many different maps can exist of the same place. Not all information about a place can be put on one piece of paper. For maps to communicate, they focus on showing a limited number of things. GIS Systems can incorporate many layers of information at the same time. 5

6 Map Reading: Important Points Mapmakers use north, south, east, and west to describe direction. Mapmakers usually orient their maps to show NORTH at the top. We use relative location to describe the relationship of one place to another. One place is north, south, east, or west of another place. Using longitude and latitude, a grid of imaginary lines created by geographers, and we can identify the absolute location of any point on the map Map Reading: Important Points Its All about Scale: The relationship between a distance on the map and the corresponding distance on the ground is known as scale A large-scale map shows a small land area in great detail. A small-scale map shows less detail, but a larger land area. Map Reading: Latitude and Longitude Imaginary lines created by mapmakers to allow them to pinpoint any place on the Earth 6

7 Map Reading: Latitude and Longitude Degrees of Longitude and Latitude are further divided: Minutes Seconds Longitude Scale Changes with Latitude: At Equator:1 longitude is 70 miles, 1 min = 1.2 miles, and 1 sec. = 0.02 miles In Idaho: 1 is about 35 miles, 1 min 0.6 miles, and 1 second is over about 50 feet. Latitude scale does not change Map Reading: Projections When we convert the round Earth to a flat map we use a projection: There are many ways the round Earth to be converted to flat maps. Some are used for sea navigation Some are for legal land descriptions Some are for relative position Map Reading: Projections 7

8 Map Reading: Projections Known UTM Position UTM Coordinates Eastings (blue line) UTM Coordinates Northings (blue line) Universal Transverse Mercator (UTM): Grid system to find position (NATO) Entire earth divided into grid (like Lat/Long) but its put into 60 zones This is based on a scale in meters north and meters east (northing and easting) Longitude & Latitude Map Reading: Projections Reading The Map: meters North meters North meters North One blue dash to the next is a travel distance of 1,000 meters (3,281 feet) Map Reading: UTM An Example USGS Topo Quad in Maryland: UTM Zone 18: Point 001 would be read as: E N E means Point 001 is in Zone 18 and it is 000 meters east of the nearest reference line (435) 8

9 Map Reading: UTM An Example Point 002 is exactly half way between 435 and 436 UTM reference marks Point 002 would be read as: E N How Far Away Are The 2 points? Map Reading: UTM An Example Point 002 is exactly half way between 435 and 436 UTM reference marks Point 002 would be read as: E N How Far Away Are The 2 points? Map Reading: UTM An Example A 2 + B 2 = C = ( ) 2 = (500,000) meters, or 2,320 feet 9