Chapter 1
Spatial Data has grown tremendously outside of the scientific world, becoming available to many other sources. GIS answers questions about why things are done the way they are and how they are related. There are two ways to evaluate spatial data, depending on the question being asked and how the information will be used. The first method contains the bigger-picture kind of information and is quicker to access, and the other kinds of methods require more digging and time to process the more specific information. The information found is typically present in many different ways, like tables, maps, etc. Depending on how information is presented, the data is either valid or useful, or it will say that more digging is needed.
To use GIS effectively, users should understand the types of geographic features represented in the software. Features on a map can be described as discrete, continuous, or summarized phenomena. Discrete features, such as specific locations, are depicted as lines or dots depending on the settings. Continuous phenomena, like weather patterns such as precipitation and temperature, are measured through equally spaced data points with no visible gaps. GIS software applies a process called interpolation to assign values to areas between these points. Continuous data can also be represented by enclosed boundaries (such as those showing soil or vegetation types), which are used to illustrate large, uniform areas of the landscape. However, these boundaries are not as definitive as discrete features. Features summarized by area primarily indicate the density within a specific boundary—for example, the number of businesses in a zip code or the number of houses within a certain radius.
Geographic features are shown through two different models, vector and raster. In a vector model, features are displayed in a table and buildings are represented as x,y locations connected with dashed lines. Raster models are presented as a matrix of cells by layer. Each layer is a specific attribute. Cell size is vital to an accurate map because if the size isn’t perfect, then information is lost.
There are five different types of attribute levels. These are types of attributes that determine how each feature is analyzed determines what level to use.
Different levels of attributes:
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- Categories – Groups of different features that are alike in some way and are represented in code or numbers.
- Ranks – Features are put in order from highest to lowest and used when features are hard to distinguish
- Counts – The count is the actual number of features on a map
- Amounts – The quantity connected to a feature
- Ratios – Comparing two quantities by dividing one by the other
Chapter 2
Chapter 2 focuses primarily on how and why features are placed where they are placed. Viewing a map now is much clearer to me because chapter helps me understand how to find patterns throughout a map. The map features are always determined based on how the information is presented and how the map is used. For instance, the police department tracks where crimes are committed and what types using GIS to better monitor high crime areas each month. Prior to placing features on a map, all features included will have geographic coordinates as longitude and latitude values and be identified as a type (must fall into a category). Mapping can occur as a single type because GIS will use the same kind of symbol and suggest that this map can be explored further. As features are added, GIS will use the applied coordinates to create lines or areas to define shapes for specific areas or smaller / single features will be drawn as a symbol defined by coordinates. Instead of laying all of the features in one layer, smaller patterns can be revealed by creating a subset which can only be represented in an underlying layer instead of just one big layer.
When one map has a multitude of categories, it is suggested that groups are created to sort the categories into smaller sets of data.
Option 1: Assign each record 2 database codes. One for detailed category and the second for its general category
Option 2: Create a table containing one record for each category corresponding to its general code. Once the map is ready to be displayed, the table and map will be linked together showing general codes with the features.
Option 3: Assigning categories by specifying the correlated symbol to go with it. Mostly used for single locations
Chapter 3
Mapping areas with the highest and lowest concentrations of specific variables is invaluable for businesses in strategic planning and market analysis. For instance, when a physician’s office considers expansion, mapping the ratio of people per existing office per mile can highlight underserved regions. This helps ensure a new location addresses real gaps in access, which increases the likelihood of success and optimizes resource allocation.
Understanding the three types of map features—discrete, continuous, and summarized—enhances how landscapes and demographic data are visualized. Discrete features pinpoint specific locations or boundaries, continuous features represent gradients like population density, and summarized features aggregate information over defined areas.
Standard classification schemes are essential tools in GIS for grouping similar data points, revealing underlying patterns, and making complex data more interpretable. These schemes rely on how the data are distributed. When data points are evenly distributed, classifications such as equal intervals or quantiles can be used for clear, balanced mapping. Charts and histograms help visualize this distribution. If the data have natural groupings or outliers, methods like natural breaks (Jenks optimization) are preferable, as they better reflect the true structure of the data.
Using GIS becomes more straightforward when data is evenly distributed, as outliers and skewed distributions can complicate analysis and visualization. Careful selection of classification methods ensures more accurate, meaningful maps that support better business decisions.
There are five ways to show quantities using GIS software:
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- Graduated symbols – includes locations, lines and areas and is best used for minimal featured maps
- Graduated colors – includes areas and continuous phenomena and makes patterns easy to read
- Charts – Used for specific locations within an area to show categories and quantities
- Contours – Used to represent rate of change across large parts of area
- D perspective views – Adds visual impacts throughout the map