An extract on #dogoftheday
The process of conversion depends on the specific situation and the intended purpose. This may be governed by regulation, contract, technical specifications or other published standards. Engineering judgment may include such factors as:
The precision and accuracy of measurement and the associated uncertainty of measurement.
The statistical confidence interval or tolerance interval of the initial measurement.
The number of significant figures of the measurement.
The intended use of the measurement including the engineering tolerances.
Historical definitions of the units and their derivatives used in old measurements; e.g., international foot vs. US survey foot.
Some conversions from one system of units to another need to be exact, without increasing or decreasing the precision of the first measurement. This is sometimes called soft conversion. It does not involve changing the physical configuration of the item being measured.
By contrast, a hard conversion or an adaptive conversion may not be exactly equivalent. It changes the measurement to convenient and workable numbers and units in the new system. It sometimes involves a slightly different configuration, or size substitution, of the item. Nominal values are sometimes allowed and used.
Cities typically have public spaces where anyone can go. These include privately owned spaces open to the public as well as forms of public land such as public domain and the commons. Western philosophy since the time of the Greek agora has considered physical public space as the substrate of the symbolic public sphere. Public art adorns (or disfigures) public spaces. Parks and other natural sites within cities provide residents with relief from the hardness and regularity of typical built environments.
Urban planning, the application of forethought to city design, involves optimizing land use, transportation, utilities, and other basic systems, in order to achieve certain objectives. Urban planners and scholars have proposed overlapping theories as ideals for how plans should be formed. Planning tools, beyond the original design of the city itself, include public capital investment in infrastructure and land-use controls such as zoning. The continuous process of comprehensive planning involves identifying general objectives as well as collecting data to evaluate progress and inform future decisions.
Government, as the ultimate wielder of force is legally the final authority on planning but in practice the process involves both public and private elements. The legal principle of eminent domain is used by government to divest citizens of their property in cases where its use is required for a project. Planning often involves tradeoffsdecisions in which some stand to gain and some to loseand thus is closely connected to the prevailing political situation.
The history of urban planning dates to some of the earliest known cities, especially in the Indus Valley and Mesoamerican civilizations, which built their cities on grids and apparently zoned different areas for different purposes. The effects of planning, ubiquitous in today's world, can be seen most clearly in the layout of planned communities, fully designed prior to construction, often with consideration for interlocking physical, economic, and cultural systems.