The Role of Space Syntax in Identifying the Relationship Between ...

The Role of Space Syntax in Identifying the RelationshipBetween Space and Crime 419of intersecting axial lines. In simple terms, the axial map is represented by the longestlines of sight that can be used to characterize every street segment in the Ypsilanti area.For example, if two people were standing at each end of the line, they will be able to seeeach other. The lines were drawn manually on top of the map using Spatialist. Ypsilanticomprised an average of 634 axial lines.Second, the program calculated the Integration and Connectivity values of every linein the system (Figure 195). To elaborate on these two measures, Connectivity gives thenumber of lines that are directly connected to a specific line. Integration, on the otherhand, is an indicator of how easily one can reach a specific line. Mathematically speaking,it is the average number of spaces that one needs to pass through to reach a specific linefrom all the axial lines in the system. In other words, these values suggest the extent towhich a selected space in the system is more integrated (can be easily reached from otherspaces), or more segregated (one has to travel through many spaces in order to reach thatselected space).Since the unit of analysis is the axial line (or the street space), it was necessary toappend sociodemographic data along with crime data to each line. Therefore, a road mapof Ypsilanti was prepared showing 21 block groups using ArcGIS. Data on populationdensity, youth concentration, level of education, percentage of owners, age distributionand racial composition were available from U.S. Census and were appended to each blockgroup in Ypsilanti. The report on crime at an address level was semi-manually enteredinto the same database (Figure 195). Moreover, the original axial map that was preparedusing Spatialist was later converted into an appropriate format and was given accurategeographic coordinates for Ypsilanti. This procedure allowed us to match the Spatialistaxial map with the ArcGIS Ypsilanti road map (Figure 196). The ‘Join Attribute’ featurein ArcGIS allowed us to merge the data on the axial map with the rest of the data.The final database that was produced in ArcGIS was later converted into an acceptableSAS format. SAS is a statistical package that enabled us conduct a Poisson Regressionmodeling of our data since the crime report was collected over a period of a year.3.3. Statistical AnalysisThe MIXED Procedure in SAS (Version 9) was used in these analyses to fit linear mixedmodels to the collected data. Because of the count nature of the response variables, squareroottransformations were performed in order to satisfy the assumptions of normality andconstant variance in random errors. In the mixed models, the fixed effects of physical andsociodemographic variables of interest on crime counts collected over one year in givenstreet-spaces or axial lines were estimated. Because of the clustered nature of the data,axial lines were clustered within randomly selected block groups, random intercepts andrandom connectivity effects associated with the randomly sampled block groups were alsoincluded, to test the hypothesis that the crime counts and effects of connectivity on crimecounts tend to randomly vary from one block group to another. Parameters in the modelwere tested using likelihood ratio tests, either based on maximum likelihood (for fixedeffects) or restricted maximum likelihood (for variance parameters associated with therandom effects).