Chapter 1:
Distinguished differences in data and emphasized the importance of being as specific as possible about the question you’re trying to answer. This is because it will help you decide how to approach the analysis, which method to use and how to present the results. There two types of models in GIS; raster and vector. In a vector model, each feature is in a row in a table, and feature shapes are defined by x,y locations in space. Features can be discrete locations or events, lines, or areas. Lines such as streams, roads, or pipelines are represented as a series of coordinate pairs. Areas are defined by borders and are represented as closed polygons. They can be legally defined or naturally occurring boundaries. Discrete features and data summarized are represented in this model. With a raster model, features are represented as a matrix of cells in continuous space. The cell size you use for a raster layer will affect the results of the analysis and how the map looks. Cell size should be based on map scale. Continuous categories are usually represented as either vector or raster. Continuous categories are represented as raster. Discrete features may also be represented by raster if you are combining them with other layers in a model since raster is particularly food for this kind of analysis.
Chapter 2:
Mapping where things are can show you where you need to take action. This allows you to explore causes for the patterns you see. Look for geographic patterns in your data to map the features in a layer using different kinds of symbols. Can also use GIS to map different types of features and see whether certain types occur in the same place. Each feature needs a location in geographic coordinates. When you map features by type, each feature must have a code that identifies its type. To add a category, you create a new attribute in the layer’s data table and assign the appropriate value to each feature. Many categories are hierarchical, with major types divided into subtypes. In some cases a single code indicates both the major type and subtype. To create a map, you tell GIS which features you want to display and what symbols to use to draw them. You can map features by category, by drawing features using a different symbol for each category value. Mapping features by category can provide an understanding of how a place functions. The GIS stores a category value for each feature in the layers data table. It also stores, separately, the characteristics of the symbols you specified to draw each value. When you display the features, the GIS looks up the symbol for each feature based on its category value and uses that symbol to draw the features on the map. Features might belong to more than one category. Using different categories can reveal different patterns.
Usually, several categories are shown on the same map. However, if the patterns are complex or the features are close together, creating a separate map for each category can make patterns within a particular category and even across categories- easier to see. Displaying a subset of categories may make it easier to see if different categories are related. If you’re showing several categories on a single map, you want to display no more than seven. Because most people can distinguish up to seven colors or patterns on a map, displaying more categories than this makes the patterns difficult to see. The distribution features and the scale of the map will also affect the number of categories you can display.
If the map contains small scattered features rather than large contiguous ones, rader will find it difficult to distinguish the various categories. If the features are sparsely distributed, you can display more categories than if the features are dense.
Chapter 3:
Mapping features based on quantities adds an additional level of information beyond simply mapping the locations of features. You can map quantities associated with discrete features, continuous phenomena, or data summarized by area. Discrete features can be individual locations, linear features, or areas. Locations and linear features are usually represented with graduated symbols, while areas are often shaded to represent quantities. Continuous phenomena can be defined areas or a surface of continuous values. Areas displayed using graduated colors while surfaces are displayed using graduated colors, contours, or a s 3D perspective view. Data summarized by area is usually displayed by shading each area based on its values or using charts to show the amount of each category. Once you’ve determined what type of quantities you have, you need to decide how to represent them on the map, either by assigning each individual value its own symbol or by grouping the values into classes. Counts, amounts, and ratios usually are grouped into classes, since each feature potentially has a different value. This is especially true if the range of values is large. Use graduated symbols to map discrete locations, lines or areas. Graduated point symbols are drawn at locations of individual features, or at the centroid of an area, to show magnitude of the data value.
Use graduated colors yo map discrete areas, data summarized by area, or continuous phenomena . Usually assign shades of one or two colors to the classes. If you have less than five or six classes, use the same color and vary the shade. Different colors have different visual impacts. Reds and oranges attract the most attention; blue-green, the least. It’s easier to distinguish between shades of blues and purples than shades of other colors.
If you have more than seven or eight classes, you may want to use a combination of colors and shades, using two or even three colors to help distinguish the classes. Warm colors for higher values . Cool colors for lower values. Using two color is also good for showing data with both positive and negative values, such as percentages above or below an average value. Use charts to map data summarized by arena or discrete location or areas. With charts, you can show patterns of quantities and categories at the same time. That lets you show more information on a map rather than showing each category on its own map.