Determination of radiation field G and density n_o from PDR Tool Box line ratio fits for the CND (left two panels), ETD (second from right), and outflow (rightmost) components using the data from Table 8. The two CND panels illustrate the sequential procedure: in the lefthand CND diagram we fit the [OI] line ratio to the intersection of the [CI] and the [CI]/CO line ratios in order to find the [OI] absorption multiplication factor and then plot the corrected [OI] and [CII] line ratios in the diagram next to it.