The subarachanoid space lies between the arachnoid and pia mater. It is filled with cerebrospinal fluid. All blood vessels entering the brain, as well as cranial nerves pass through this space. The term arachnoid refers to the spider web like appearance of the blood vessels within the space.
Why do biologists organize living things into groups? What do the levels of classification indicate about the relationship between organisms? What characteristics are used to classify organisms into domains and kingdoms? What is the scientific study of how living things are classified called? Taxonomy
From Wiki.GIS.com. Classification is the process of data analysis used to make choropleth maps. It arranges data according to the values of information and allows the cartographer to recognize patterns in the data. Changing the classification of a data set can create a variety of different maps. There are five major classification types: Equal Interval classification, Quantile, Jenks Natural Breaks Classification, Geometric Interval Classification, and Standard Deviation.