(In this example we are pretending that there are no strata, so there is no stratum name or stratum area column. So, if there were 2 birds seen in 0-50, 3 at 50-100 and 3 at 100-200 on point 1, then the data file would look like this: To enter this type of data into Distance, enter each observation at the mid-point of the interval. For example, in a point transect survey of songbirds one could define intervals of 0-50 metres, 50-100, and 100-200. Instead, observations are placed in pre-defined intervals, or bins. In some distance sampling surveys, the exact distances to the observations are not recorded. This is the default end-of-line indicator used by most windows-based applications, so you usually don’t have to worry about this. Each row should finish in a Carriage-return + Line-feed combination. The order of the columns is not important, as you tell Distance which column is which during the import process. The columns should be separated by a delimiter (ASCII character), which can be either a tab, semicolon, comma or space. So, you will end up with somewhere between 2 and 7 columns, depending on the type of survey. If you measured radial distance and angle then you will need a column for angle, and if your objects are clusters, rather than individuals, then you should include a column for cluster size. If your survey involved stratification then you will need to include columns for stratum name and stratum area. For line transect surveys you will also need a column for transect length. Which columns should you include in your data file? As a minimum, your file should contain a column for transect or point name and a column for observed distance. The video is 8 minutes in length and provides you with requisite information to import simple data structures into Distance. There is a narrated video that describes the sequences of instructions you provide to Distance to bring these data into Distance for analysis. Notice also that the record “Line 1” in “Stratum 2” has no distance in the final column – this is a transect where no objects were seen. Notice that all transects from the same stratum are grouped together on adjacent lines, and all observations from the same transect are grouped together. Column 1 is the stratum name, column 2 is the stratum area, column 3 is the transect name, column 4 is the transect length, and column 5 is the perpendicular distance.
In this file, the columns are separated by semicolons. Here’s an example of part of a data file, from a line transect survey with two strata: The actual number of columns depends on the type of survey (see later).
To import a data file into Distance, it must be in “flat file format” – i.e., arranged in rows and columns with one row for each observation. However, most people will already have their data on computer, for example in a spreadsheet or database file, and in this case it is easiest to turn it into a text file and import this file into Distance. If you only have relatively few observations then it may be easiest to re-enter the data from the keyboard. You can get data into a project file either by entering it from the keyboard or by importing it from a text file. In Distance, all of your data and analyses are kept in a “project file”. If you have not got any data to bring along then don’t worry – we will be providing plenty of informative exercises to keep you busy during the computer sessions! Also, there may well be someone with similar interests to you who has brought some data along, so you could discuss the analysis together.
If you are already using Distance 6 (the current versions) then feel free to bring along your data and analyses as a Distance project file. If you can bring your data to the workshop in this format then we will be able to import it quicker, and so you will have more time to play with the analysis.
This page explains how to get your data into a format that Distance can easily read. One of the goals of the workshop is to enable people who have already collected distance sampling data to do some preliminary analysis of their data using the computer program Distance.