Tuesday, February 26, 2008

Bolstad Chapter 4- Data Sources and Data Entry

There are many sources of spatial data which can be divided into 2 forms: hardcopy and digital. Hardcopy forms include any drawn, written, or printed documents and were the most common storage for spatial data until the 1980s when GIS came onto the scene in a major way. Digital forms of spatial data are those in computer-compatible format. Digital data are often from hardcopy maps that have been converted over to digital format. The chapter goes into specifics about the process of digitizing data.

This chapter also talks about different types of maps such as feature, choropleth, dot-density, and isopleth (or contour) maps as well as map scale and map generalization.

Tuesday, February 19, 2008

Sunday, February 17, 2008

Digital data

This is a summary of the Chapter 7 lecture on digital data.

There are 4 things we need to consider with digital data:
1. who produces the data?
2. is it vector or raster data?
3. what is the scale and accuracy of the data?
4. what is the content of the data?
* also, data is not usually in the shape and size you need. have to manipulate it for your purpose.

There are many different digital data sources:

* NLCD (National Land Cover Datasets)
*DRG (Digital Raster Graphic)
*DLG (Digital Line Graphs)
*DOQ (Digital Orthophoto Quads)
*National Wetlands Inventory (NWI)
*Digital Soils Data

*DEM (Digital Elevation Models)- these are really neat; raster data set, resolution is down to 20' b.c of recent flooding and the need to better map flood zones, each cell has a value of elevation, derived from LIDAR, it's the highest resolution data we've ever had for elevation-type stuff, *hillshade is cool*

*Buncombe County Digital Data?

* TIGER/Census data (Topologically Integrated Geographic......)

Chapter 13

Saturday, February 9, 2008

Chapter 3 lecture

This lecture kinda blew my mind; it was the first time I'd ever heard the word datum before (that I know of). So a lot of terminology and concepts were new and somewhat intimidating. But now that I've done the ESRI tutorial, read some in the book, and gone over my lecture notes again... I'm starting to get it. It really did take 3 times of pouring over the same information, but in different formats, for it to sink in. The sinking in part is exciting though, and here's a very brief summary of some things, but not everything.

Geodesy is the study of the size and shape of the Earth. Sounds simple enough- but it's not! There are spheroids and ellipsoids involved (apparently the same thing) which are smooth mathematical models of the Earth, while a geoid is a geographic model of the Earth which approximates gravitational pull. Datums are a set of coordinate locations which have been measured horizontally or vertically and tell us the latitude and longitude of a set of points on an ellipsoid. Also called a reference surface. Some common ones are NAD 27 and NAD 83. Projecting maps is whole other monster which always involves distortion of one or all of these: shape, area, distance, and direction. Here in the US we are likely to use either the Lambert Conformal Conic or the Universal Transverse Mercator projections. Counties often use State Plane as their projection of choice. North Carolina only has one state plane, but many states have more than one. Now I need to study for tomorrow's test...

Sunday, February 3, 2008