tailieunhanh - Practical GIS Analysis - Chapter 3

Điểm A là một GIS X, Y vị trí mà không có diện tích hoặc chu vi. Ví dụ các chủ đề điểm bao gồm các điểm địa điểm từ lô nghiên cứu, phát thanh-động vật có cổ, giếng nước, cây cá nhân, vòi nước chữa cháy, hoặc cột điện. Các công cụ GIS sau đây có thể được sử dụng trong việc quản lý điểm: • ADDXY-Bổ sung thêm điểm X, Y phối hợp như các mặt hàng mới trong bảng thuộc tính điểm. • NODEPOINT-Tạo một chủ đề điểm mới từ các nút trong một đường dây hoặc. | Chapter 3 Point Analysis INTRODUCTION A point is a GIS X Y location that has no area or perimeter. Example point themes include point locations from research plots radio-collared animals wells individual trees fire hydrants or utility poles. The following GIS tools can be used in managing points ADDXY Add each point X Y coordinate as new items in the point attribute table. NODEPOINT Create a new point theme from nodes in a line or polygon theme. ARCPOINT Create a new point theme from arc vertices or polygon labels in a line or polygon theme. POINTNODE Transfer attributes from points to the nearest node in a line or polygon theme. Points can be analyzed using the following GIS tools AREA ANALYSIS TOOLS THIESSEN Create polygons of proximity from points. BUFFER Generate buffer areas of a user-specified distance around points. DISTANCE ANALYSIS TOOLS NEAR Compute the nearest distance from points to features in a second point line or polygon theme. POINTDISTANCE Compute all point distances between two point themes. ATTRIBUTE ANALYSIS TOOLS RESELECT Create a new point theme by selecting points using a logical expression. INTERSECT Transfer polygon attributes to a point theme. 27 2002 Taylor Francis 28 Practical GIS Analysis AREA ANALYSIS TOOLS THIESSEN Converts a point theme into a theme of proximal or Thiessen polygons Thiessen polygons can be used to apportion a point theme into polygons known as Thiessen or Voronoi polygons. Each polygon will represent only one point s region. Each polygon has the unique property that any location within that polygon is closer to the polygon s source point than to any other points. Let s do the following example. Step 1 Connect the points 1 to 2 2 to 3 3 to 4 and 4 to 1 with dashed lines. Step 2 Draw the midpoint of each line. Step 3 Draw a solid line at each midpoint perpendicular to your dashed lines. Each solid line represents the distance halfway between two points. Draw these lines until they merge to create polygons. Erase your