171 Concepts and Definitions
13.8.3 Unpaid family Worker: Is a member of a family of the owner/owners of an establishment, usually working for the establishment without payments.
13.9 Total Persons Engaged This is the total labour force comprising of operatives, other employees, work ing proprietors and unpaid workers.
13.10 Capital Investment Refers to money invested in a business with the understanding that the money will be used to purchase fixed assets, rather than used to cover the business' day-to-day operating expenses. 13.11 Annual Turnover Refers to total amount of money earned by a business for a particular period of time
172 Concepts and Definitions
CHAPTER FOURTEEN
GEO-INFORMATION SYSTEM /SPATIAL DATA
14.0 Geographical Information System (GIS)
Geographical Information System (GIS) is a system of hardware, software and procedures
designed to support the capture, management, manipulation, analysis and display o f geo -
referenced maps and data.
The Geo-Information Section is already developing a digital geographic database, but a full GIS
is a very expensive and complex technology that needs to be implemented only at a level
appropriate to the skills and resources available.
14.1 Maps
Maps refer to a scientific and technical representation of physical and manmade features of the
earth's surfaces/land parcel onto a flat surface/sheet of
paper with respect to specified scale.
A map is generally small enough to be handled easily,
yet it can show a large area. It permits a person to
view at a glance those features that he might find
difficult to see physically due to limitations imposed
by his/her size or his/her location.
There are many kinds of maps, each serving a specific
purpose. There are maps that show the location of
cities and rivers. There are soil and land use maps,
geological and to pographic maps, cadastral maps,
navigation maps, weather maps, administrative maps,
road maps, transportation route maps, city maps and individual property maps. A map shows
part or the Earth’s entire surface. It shows the real world at a reduced scale; that is, the real world
is compressed into a small area on the map. The extent of reduction influences the kind of
features and amount of detail that can be shown.
14.1.1 Base Map
A Base Map is a map depicting background reference information such as landfor ms, roads,
landmarks, and political boundaries, onto which other thematic information is placed. A base
map is used for locational reference and often includes a geodetic control network as part of
its structure. A base map provides a user with context for a map. You can add information to
a base map by overlaying other information on top of it. Base maps contain reference
173 Concepts and Definitions
information that may provide different geospatial information based on what the cartographer is trying to communicate.
14.1.2 Physical Map A physical map is one that shows the physical landscape features of a place. They generally show things like mount ains, rivers and lakes and water is always shown with blue. Mountains and elevation changes are usually shown with different colors and shades to show relief.
14.1.3 Topographic Map A topographic map is a detailed and accurate two -dimensional representation of natural and human-made features on the Earth's surface. The most distinctive characteristic of a topographic map is that the three -dimensional shape of the Earth's surface is modeled by the use of contour lines. Contours are imaginary lines that conn ect locations of similar elevation. Contours make it possible to represent the height of mountains and steepness of slopes on a two-dimensional map surface. A topographic map is similar to a physical map in that it shows different physical landscape features. They are different however because they use contour lines instead of colors to show changes in the landscape.
Topographic maps produ ced by the Tanzania Surveys and Mapping Division are generally available in two different scales: 1:50,000 and 1:25,000. Maps with a scale of 1:25,000 are relatively large-scale. At this scale, features as small as a single home can be shown. The smaller s cale 1:50,000 topographic map is more of a general purpose rec onnaissance-type map.
14.1.4 Thematic Map A thematic map is a map that focuses on a particular theme or special topic. An example of a thematic map would be one showing the population change of Tanzania in specific locations from 1998 to 2012.
14.1.5 Census/Survey Maps Census maps r efer to the smallest geographic area from which census/survey data are collected. They are usually called Enumeration Areas (EAs). The process of creating and marking EA boundaries on the base map is called delineation. EA delineation team does this work. The same team also designates the Supervision Areas (SAs).
Base maps currently being used by the NBS for creating enumeration areas are produced by the Surveys and Mapping Division of the Ministry of Lands and Human Settlements Development. The country is covered by 1:50,000 topographic base maps (about 1265
174 Concepts and Definitions
sheets). Other base maps include 1:2,500 maps used in cities and towns, 1:250,000 district maps.
14.1.6 Supervisor Area Maps The maps refer to an area covered by one supervisor during censuses and surveys. A Supervisor Area (SA) map contains enumeration area (EA) boundaries delineated on it. It contains information on the number of enumeration areas under that su pervisor. The map is used by the enumeration supervisor in planning his/her travel to observe the enumerators and review their work and verify boundaries so as to ensure that there is no omission and no duplication of area.
14.1.7 Statistical Maps These r efer to maps showing the spatial distribution of statistical data. The purpose is to present significant statistical results in terms of their geographic distribution. Thus interest in the current pattern of distribution and also in changes in the patterns that have occurred over time, particularly since the last census/similar survey is considered.
14.1.8 Point Symbol Maps Point symbol maps refer to dots or graduated symbols used in representing a certain value on the statistical map.
14.1.9 Choropleth (Shaded) Maps Choropleth maps refer to administrative areas colour shaded to present several classes of statistical data, such as densities, per capita, ratio of one characteristic to another, etc.
14.1.10. Isopleth Maps These refer to maps representing statistical data by a series of lines each connecting points at which a given variable has a specific value.
14.2 Map Elements
14.2.1 Scale Scale refers to the relationship between the distance on the map as compared to the distance on the ground. By using the scale, census or any other survey staff can determine distances required for field checking, for conducting enumeration, etc. The scale should always be shown on census/survey maps. A Scale may be expressed in three ways: (a) Word statement, (b) Numerical fraction, and
175 Concepts and Definitions
(c) Graphic scale. Graphic scale is commonly used in census/survey maps. A graphic or bar scale shows the relationship between distances on the map and on the ground by means of a bar or line, with markings to indicate distances on the ground.
14.2.2 Map Symbols Map symbols refer to figures, lines, colours, or patterns used to indicate certain features on the ground such as administrative boundaries, buildings, rivers, roads, railroads, etc. Symbols are used to show three different t ypes of information; (a) location (b) nature or quality of the features, and (c) Quantity. Maps normally show what features are and where they are as the primary function. Maps showing how much there is of var ious features are primarily statistical maps.
14.2.3 Other Map Elements Refer to; (a) Grid coordinates: describe all points on the Earth. (b) Type of projection: indicates the amount and kind of distortion of the features. (c) North arrow: orients the map by compass directions (d) Date of the map: reveals how current it is. (e) Source of the original materials: give the idea of reliability and accuracy of the map. (f) Sheet number: helps in locating other maps for the same area.
14.3 Codes Codes refer to uniquely identification by number of al l administrative divisions of every order for which data are to be tabulated. This is made possible by the use of unique numbers assigned to them. Tanzania (Mainland and Zanzibar) has 26 regions, which are divided into districts and further subdivided into wards and villages. 14.3.1 Regional and District Codes Regional and District Codes refer to a two-digit number identifying an administrative region and district; with each respective code having two digits.
14.3.2 Ward/Shehia Code Ward/Shehia Code refers to an administrative ward or shehia. A ward/shehia code has three digits. The first two digits stand for a serial number of the ward within the district, the third digit classifies the ward/she hia into whether it is pure rural (1), pure urban (2) or mixed (3). For example, ward/shehia 031 means third ward/shehia in a district which is pure rural; 072 means seventh ward/shehia which is pure urban; and 113 means eleventh ward/shehia which is mixed, that is, part of it is rural while the rest of it is urban.
176 Concepts and Definitions
14.3.3 Village/Mtaa Code Village/Mtaa Code refers to a two-digit number identifying an administrative village/mtaa.
14.3.4 EA Code EA Code refers to a number identifying the smallest geographic area from which census/survey data are collected. EA code has twelve-digits which is a collection of all levels of administration including the number of and EA which has three digits. That is, an EA code comprises two-digit regional code, two-digit district code, three-digit ward/shehia code, two-digit village/mtaa code and a three-digit EA number.
14.4 Aerial Photography It refers to a process of recording features on the earth using remote sensing instrument(s).
14.5 Satellite Imagery
Satellite imagery r efers to the collection of information through satell ites, that is, information
collected from an altitude of 320 kilometers (200 miles) or more. Unmanned satellites, such as
Land sat 1 and 2, pass over the entire inhabited Earth many times on a regular basis, providing
almost complete coverage of the Earth’ s surface. The sat ellites use a particular sensors or
scanners to sense or scan the amount of energy being reflected or radiated from a series of points
into numerical values, and radio these values to receiving stations on the Earth. The values are
then processed to make pictures for use in the usual interpretation.
14.6 Global Positioning System (GPS)
It r efers to space-based navigation system that provides location and time information in all -
weather conditions anywhere or near the earth.
14.7 Automated Cartography
Automated cartography r efers to the map production process using computers, automatic
drafting equipment, and microfilm systems. The development of automated cartography
increases the speed and accuracy while reduces the cost of map product ion. Automated
cartography depends on the availability of computer readable coordinates associated with
specific geographic unit. Each point on a map must be identified and recorded in machine -
readable form, producing a computer file, and once the basic fi le is created, it can be easily
updated.
177 Concepts and Definitions
CHAPTER FIFTEEN
SAMPLING
Sampling refers to drawing a sample or selecting a subset of elements from a population. The
usual goal in sampling is to produce a representative sample. A sample is equivalent to the
population on all characteristics, except that it includes fewer elements. A perfect representative
sample would be a “mirror image “of the population from which it was selected, except it would
include fewer elements. The selection of a sample can eithe r be through probability or non -
probability mechanism.
15.0 Population Refers to the totality of the elements under study or entire group of units, which is the focus of the study. For example, population could consist of person or non – human units such as farms, houses or establishments such as industry, schools and hospitals.
15.1 Target population The set of elements about which information is wanted and estimates are required. Practical considerations may dictate that some units are excluded (e.g. Institutionalized individuals, the homeless, or those who are not be possible to access Without incurring excessive cost).
15.2 A Sample A set of elements taken from a population.
15.3 A Statistic A numerical characteristic of a sample.
15.4 Parameter A numerical characteristic of population.
15.5 Response rate Percentage of sampled units who actually participate in the study.
15.6 Domain of the Study Refers to a major segment of the population for which separate statistics are needed. A domain can be either a geographical area or a specified population category, such as a region or major ethnic groups. Domains are very important for the determination of a sample size and sampling distribution of statistics
178 Concepts and Definitions
15.7 Sampling Frame Refers to a list of units from which a sample is to be selected. It must have characteristics to be studied.
15.8 Sampling Unit It is a smallest unit or element, which is the subject of sample selection or a unit of analysis, such as a person, household or an establishme nt. Sampling unit may be Primary, secondary, e.t.c. depending on the stages of sampling.
15.9 Estimation Refers to the process of estimating population characteristics based on the sample statistics. The characteristics may be any variable associated wi th a member of the population, such as age, income, employment status and the quantity may be a total, proportion, average and standard deviation.
15.10 Statistical Error The difference between the true population parameters and the estimated statistics from a sample.
15.11 Sampling Error Refers to an inaccuracy in the estimates of the population characteristics which arise due to the sample on which the estimates are made from.
15.12 Non – Sampling Error Refers to inaccuracy which occurs when estimating population characteristics due to defective measurement techniques, mistakes during data collection, processing and interpreting, etc.
15.13 Sampling Procedure Refers to the approach followed to select sampling units or elements from the population: It includes non – probability sampling or probability sampling.
(i) Non – Probability Sampling Refers to the selection of sampling units without using probability mechanism . It covers a variety of procedures, including the use of volunteers and the purpo sive choice of elements for the sample on the grounds it is a “representative” of a population.
(ii) Probability sampling Refers to the selection of sampling units by using probability mechanism . An essential requirement for any form of probability sampling is the existence of a sampling frame or population from which the sampled elements are selected from . Probability Techniques widely used are: Simple Random Sampling; Systematic
179 Concepts and Definitions
Sampling; Stratified Sampling; Cluster Sampling; Multistage Sampling and Probability Proportional to Size Sampling.
15.14 Simple Random Sampling Refers to the selection of sampling units of size n from the population of size N. In Simple Random Sampling, each element has an equal chance of being selected
15.15 Stratified Random Sampling (or Stratified sampling) Refers to the method of selecting a sample from a population of size N where the population is firstly sub – divided into k sub – populations called strata;
First, stratify your sampling frame (e.g. divide it into the low, medium, high income households or males, females depending on your stratification variable).
Second, take a random sample from each strata (i.e. take random samples from a low income households, medium income households, high income households, or ma les, females. The selected random samples will constitute the final sample. (Note: you could also take Systematic samples from respective strata).
15.16 Systematic Random Sampling (or Systematic Sampling)
In this sampling method the N units in the sampli ng frame are arranged in a particular order
Suppose N = nk, where n is the sample size and k is an integer, a random number less than or
equal to k is selected and thereafter every kth element is selected.
15.17 Cluster Sampling Refers to the process of firstly selecting a number of clusters from a sampling frame cons isting of all clusters. A study is then carried out to all units in the entire selected clusters . For example, select geographical areas first and within the selected geographical areas, all households are interviewed
15.18 Multistage Sampling Refers to the process where selection of the sample is carried out in stages. For example, select geographical areas first and within the selected geographical areas, select households to be interviewed.
15.19 Quota Sampling Refers to a method of selecting a sample in which investigator collects information from individuals until the sample size (the quota) is attained.
180 Concepts and Definitions
15.20 Probability Proportional to Size Sampling Refers to the selection of (both primary and secondary) sampling units based on the sizes of the sampling frames . The process of selecting sampling units follows the principal of Multistage Sampling.
15.21 Primary sampling unit (PSU) Geographical area comprising one or more enumeration areas of the same type (and therefore not necessarily contiguous) that together have at least one hundred dwelling units.
15.22 Sampling Weight Refers to the process of improving survey results by m aking adjustments for total non -response, to conform to the known population distribution in order to improve precision of sample estimates and analysis of data obtained from a complex sample surveys.
15.23 Adjustment for statistical purposes A set of procedures employed to improve coverage, classification, timing or valuation of the data, conform to an accounting or recording basis, or address data quality differences in compiling specific datasets.
15.24 Administered item Registry item for which administrative information is recorded in an administration record.
15.25 Administration record Collection of administrative information for an administered item.
15.26 Administrative data The set of units and data derived from an administrative source.
15.27 Administrative source A data holding containing information collected and maintained for the purpose of implementing one or more administrative regulations.
15.28 Bias An effect which deprives a statistical result of representativeness by systematically distorting it, as distinct from a random error wh ich may distort on any one occasion but balances out on the average.
15.29 Code A language-independent set of letters, numbers or symbols that represent a concept whose meaning is described in a natural language.
181 Concepts and Definitions
15.30 Coding The process of converting verbal or textual information into codes representing classes within a classification scheme, to facilitate data processing, storage or dissemination.
15.31 Cold deck The imputation technique used during data editing where missing or inconsistent values are calculated or derived from other information about the household or person. Synonym logical imputation. See hot deck.
15.32 Coverage The definition of the population that statistics aim to cover.
15.33 Coverage error Error caused by a failure to ad equately cover all components of the population being studied, which results in differences between the target population and the sampling frame.
15.34 Data
A representation of facts, concepts, or instructions in a formal manner, suitable for
communication, interpretation, or processing by humans or by automatic means.
15.35 Data confidentiality
A property of data, usually resulting from legislative measures, which prevents it from
unauthorised disclosure.
15.36 Data editing Activity aimed at detecting and correcting errors, logical inconsistencies and suspicious data.
15.37 Data imputation The procedure of entering a value for a specific data item , where the response is missing or unusable.
15.38 Data processing The operation performed on data in o rder to derive new information according to a given set of rules.
15.39 Hot deck The imputation technique used in data editing where the source for imputed values is constantly updated from valid response combinations encountered during processing, thus reflecting the reality of the households and persons most recently processed. Synonym: dynamic imputation. See cold deck.
182 Concepts and Definitions
15.40 Item response rate The ratio of the number of eligible units responding to an item to the number of responding units eligible to have responded to the item.
15.41 Macro data Observation data gained by a purposeful aggregation of statistical micro data.
15.42 Matching An operation whereby households and individuals enumerated during a census and a post- enumeration survey are compared for similarities and differences.
15.43 Metadata Data about data, that refers to the definitions, descriptions of procedures, system parameters, and operational results which characterise and summarise statistical programs.
15.44 Micro data Observation data collected on an individual object or statistical unit.
15.45 Probing The technique that is used to obtain a complete and relevant response by asking further questions.
15.46 Questionnaire A group or sequence of questions designed to elicit information upon a subject, or a sequence of subjects, from an informant.
15.47 Random number A number allocated to a statistical unit that is mainly used for sampling purposes.
15.48 Reference period The period of time (day, week, month, or year) for which information is relevant
15.49 Refusal Situation when a household or individual refuses to answer the questions or complete the questionnaire.
15.50 Respondent The person or organisation that answers the questions or completes the questionnaire.
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